Ultra-thin polymer film, and porous ultra-thin polymer film

ABSTRACT

The objective of the present invention is to provide a porous ultra-thin polymer film, and a method for producing said porous ultra-thin polymer film. The present invention provides a porous ultra-thin polymer film with a film thickness of 10 nm-1000 nm. In addition, the present invention provides a method for producing a porous ultra-thin polymer film, comprising the steps of: dissolving two types of mutually-immiscible polymers in a first solvent in an arbitrary proportion to obtain a solution; applying the solution onto a substrate and then removing the first solvent from the solution applied onto the substrate to obtain a phase-separated ultra-thin polymer film that has been phase-separated into a sea-island structure; and immersing the ultra-thin polymer film in a second solvent which is a good solvent for the polymer of the island parts but a poor solvent for a polymer other than the island parts to remove the island parts, thereby obtaining a porous ultra-thin polymer film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of international application numberPCT/JP2013/056823, filed on Mar. 12, 2013, and claims the benefit ofpriority under 35 USC 119 of Japanese patent application number2012-054255, filed on Mar. 12, 2012, which are incorporated herein byreference.

TECHNICAL FIELD

the present invention relates to an ultra-thin polymer film, afree-standing porous ultra-thin polymer film and else.

BACKGROUND ART

Ultra-thin films of organic molecules are conventionally prepared by aspin-coating technique, an electrolytic polymerization technique, avapor deposition technique, a vapor deposition polymerization techniqueor the like. In addition, Langmuir-Blodgett (LB) method is well known asa method for obtaining an alignment layer. According to this method:amphiphilic molecules are dissolved in a volatile organic solvent anddeposited at a gas-liquid interface; the solvent is evaporated to becompressed; and the resultant monomolecular layer is transferred onto asolid substrate. This method allows the control of the number of thethin film layers and the order of the laminated layers. Also known are amethod in which polymerizable functional groups are introduced intoamphiphilic molecules to form an ultra-thin film by LB method which isthen polymerized for stabilization, and a method in which an ultra-thinfilm is obtained by LB method from already polymerizedhigh-molecular-weight amphiphilic molecules or amphiphilic blockcopolymers.

Moreover, for a free-standing ultra-thin polymer film having anarbitrary shape, for example, a method in which a self-assembledmonomolecular layer is formed on a gold substrate that has a patternacquired by microlithography technique, then polymerizable molecules areadsorbed and polymerized in water and the formed ultra-thin polymer filmis peeled off from the gold substrate, and a method in which polymerelectrolytes are alternatively laminated on a substrate to form anultra-thin polymer film and then the ultra-thin film is peeled off fromthe substrate by using an aqueous support membrane to prepare anultra-thin film having the same size as the substrate are known (see,for example, Patent Document 1: WO 2006/025592, Patent Document 2:WO2008/050913, etc.).

Meanwhile, a composite membrane made of a plurality of polymers or blockcopolymers is known to have a micro-phase-separated structure whichincludes spherical, columnar, lamellar and gyroidal structures. Forexample, a method in which a micro-phase-separated columnar structureformed with an amphiphilic block copolymer is utilized so as todecompose and eliminate the polymer forming the columns by means ofplasma, light, an electron beam, heat, an acid, a base, a reductant orthe like, thereby obtaining a porous film is known (see, for example,Patent Document 3: Japanese Unexamined Patent Application PublicationNo. 2003-155365, Patent Document 4: Japanese Unexamined PatentApplication Publication (Translation of PCT) No. 2004-502554, PatentDocument 5: Japanese Unexamined Patent Application Publication No.2004-124088, Patent Document 6: Japanese Unexamined Patent ApplicationPublication No. 2010-116463, etc.).

When an amphiphilic polymer solution is applied onto a glass substrateor the like and humid air is sent upon preparing a cast film, latentheat is released upon evaporation by which the moisture builds upcondensation, leaving homogeneous array of droplets on the solution.According to a known method, these self-assembled droplets serve astemplates to give clearly opened pores with a constant size of fewmicrons in a polymer film, thereby forming a thin polymer film having ahoneycomb structure (see, for example, Patent Document 7: JapaneseUnexamined Patent Application Publication No. 2006-70254, etc.).

Since porous films that utilize such an above-describedmicro-phase-separated structure use polymers having a particular kind ofstructure such as block copolymers or amphiphilic polymers, they lackedversatility. Furthermore, use of a general polymer for obtaining aporous ultra-thin polymer film having a plurality of pores in afree-standing ultra-thin organic polymer film has been unknown. Inaddition, a method for producing such a porous ultra-thin polymer filmhas also been unknown.

Here, claim 1 of Patent Document 8 states a method for producing aporous film, comprising the steps of: applying an application liquidcontaining an organic compound and a hydrophobic organic solvent onto asupport to form a coating layer; and condensing water vapor on thecoating layer to dry the coating layer (i.e., condensing and dryingsteps).

In addition, claims 1 of Patent Documents 9 and 10 state a porous filmcomprising a micro-phase-separated structure including a continuousphase having a water-insoluble polymer A as the primary component and acylindrical microdomain having a water-soluble polymer B as the primarycomponent, wherein cylindrical micropores with an average pore diameterof 1-1000 nm are present in the cylindrical microdomain.

Moreover, Example 2 of Patent Document 11 describes that a substanceresulting from PMMA deterioration is removed from an asymmetricdiblock/copolymer film made of polystyrene (PS) and polymethylmethacrylate (PMMA) formed on a gold film to prepare a PS nanoporetemplate.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] WO2006/025592

[Patent Document 2] WO2008/050913

[Patent Document 3] Japanese Unexamined Patent Application PublicationNo. 2003-155365

[Patent Document 4] Japanese Unexamined Patent Application Publication(Translation of PCT) No. 2004-502554

[Patent Document 5] Japanese Unexamined Patent Application PublicationNo. 2004-124088

[Patent Document 6] Japanese Unexamined Patent Application PublicationNo. 2010-116463

[Patent Document 7] Japanese Unexamined Patent Application PublicationNo. 2006-70254

[Patent Document 8] Japanese Unexamined Patent Application PublicationNo. 2011-105780

[Patent Document 9] Japanese Unexamined Patent Application PublicationNo. 2010-138286

[Patent Document 10] Japanese Unexamined Patent Application PublicationNo. 2009-256592

[Patent Document 11] Japanese Unexamined Patent Application PublicationNo. 2004-502554

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present invention has an objective of providing a free-standingporous ultra-thin polymer film, a method for producing a porousultra-thin polymer film and the like.

Means for Solving the Problem

In order to solve the above-described problem, the present inventorshave gone through intensive studies and in consequence conceived that aporous polymer can be produced by mixing a polymer solution with a poorsolvent which is compatible with the solvent for the polymer solutionand whose boiling point is higher than that of said solvent for thepolymer solution, casting the resultant on a substrate to obtain anultra-thin polymer film that has been phase-separated into a sea-islandstructure, and further evaporating the poor solvent making up the islandparts, and that alternatively a porous ultra-thin polymer film can beproduced by dissolving two types of polymers that are mutuallyimmiscible in solid states in a common solvent, casting the resultant ona substrate to obtain an ultra-thin polymer film that has beenphase-separated into a sea-island structure and treating it with a goodsolvent for the polymer making up the island parts so that only theisland parts are removed from the ultra-thin polymer film, therebyaccomplishing the present invention.

Specifically, the present invention provides the following free-standingporous ultra-thin polymer film and a method for producing the same.

[1] A free-standing porous ultra-thin polymer film having a filmthickness of 10 nm-1000 nm.

[2] The porous ultra-thin polymer film according to [1] above, whereinthe pores with a size of 30 nm-50 μm are present on the surface at adensity of 5×10⁻³ pores/μm²-50 pores/μm².

[2a] The porous ultra-thin polymer film according to [1] above, whereinthe size of the pores is in a range that is larger than 1 μm and smalleror equal to 25 μm.

[2b] The porous ultra-thin polymer film according to [2a] above, whereinthe size of the pores is in a range that is smaller or equal to 15 μm.

[3] The porous ultra-thin polymer film according to either one of [1] or[2] above, wherein the pore diameter distribution is at least ±20%.

[3a] The porous ultra-thin polymer film according to either one of [2a]or [2b] above, wherein the pore diameter distribution is at least ±20%.

[4] The porous ultra-thin polymer film according to any one of [1], [2]and [3] above, wherein the ratio of the pore diameter to the filmthickness of the porous ultra-thin polymer film (pore diameter (μm)/filmthickness (μm)) is 0.1-50.

[4a] The porous ultra-thin polymer film according to any one of [2a],[2b] and [3a] above, wherein the ratio of the pore diameter to the filmthickness of the porous ultra-thin polymer film (pore diameter (μm)/filmthickness (μm)) is 0.1-50.

[5] The porous ultra-thin polymer film according to any one of [1], [2],[3] and [4] above, wherein the polymer is at least one selected from thegroup consisting of polyhydroxyalkanoic acid, a copolymer ofpolyhydroxyalkanoic acid, polyester-ether), a polyester of aliphaticdicarboxylic acid and aliphatic diol, polyamide, polyurethane,polysaccharide ester, poly(acrylate), poly(methacrylate), polystyrene,polyvinyl acetate and polysiloxane.[5a] The porous ultra-thin polymer film according to any one of [2a],[2b], [3a] and [4a] above, wherein the polymer is at least one selectedfrom the group consisting of polyhydroxyalkanoic acid, a copolymer ofpolyhydroxyalkanoic acid, poly(ester-ether), a polyester of aliphaticdicarboxylic acid and aliphatic diol, polyamide, polyurethane,polysaccharide ester, poly(acrylate), poly(methacrylate), polystyrene,polyvinyl acetate and polysiloxane.[6] A method for producing a porous ultra-thin polymer film, comprisingthe steps of:

dissolving two types of mutually-immiscible polymers in a first solventin an arbitrary proportion to obtain a solution;

applying the resulting solution onto a substrate and then removing thefirst solvent from the solution applied onto the substrate to obtain anultra-thin polymer film that has been phase-separated into a sea-islandstructure; and

immersing the ultra-thin polymer film in a second solvent which is agood solvent for the polymer of the island parts but a poor solvent forthe polymer other than the island parts to remove the island parts,thereby obtaining a free-standing porous ultra-thin polymer film with afilm thickness of 10 nm-1000 nm.

[6-2] The method according to [6] above, wherein the island parts of thesea-island structure have a size in a range that is larger than 1 μm andsmaller or equal to 25 μm, and are present on the surface at a densityof 5×10⁻³ pores/nm²-50 pores/gm².

[6-3] The method according to [6-2] above, wherein the size of theisland parts of the sea-island structure is in a range that is smalleror equal to 15 μm.

[6-4] The method according to any one of [6], [6-2] and [6-3] above,wherein the film thickness of the ultra-thin polymer film is 10 nm-1000nm.

[6-5] The method according to any one of [6], [6-2], [6-3] and [6-4]above, wherein the combination of the first polymer forming the islandparts of the sea-island structure and the second polymer forming the seaparts is selected from the following group:

(i) first polymer: polystyrene, and second polymer: polymethylmethacrylate;

(ii) first polymer: polystyrene, and second polymer: poly-D/L-lacticacid;

(iii) first polymer: polymethyl methacrylate, and second polymer:polystyrene;

(iv) first polymer: polyethylene glycol, and second polymer:polystyrene;

(v) first polymer: polyvinylpyrrolidone, and second polymer:polystyrene; and

(vi) first polymer: poly-D/L-lactic acid, and second polymer:polystyrene.

[7] A method for producing a porous ultra-thin polymer film comprisingthe steps of:

dissolving a polymer as a raw material in a mixed solvent containingarbitrary proportions of a good solvent for said polymer and a poorsolvent whose boiling point is higher than that of said good solvent toobtain a solution; and

applying the resulting solution onto a substrate and removing the mixedsolvent from the solution applied onto the substrate to obtain afree-standing porous ultra-thin polymer film having a film thickness of10 nm-1000 nm.

[8] A method for producing a free-standing porous ultra-thin polymerfilm having a film thickness of 10 nm-1000 nm, the method comprising thesteps of:

dissolving a polymer in a solvent to obtain a solution;

applying the solution onto a textured substrate and then removing thesolvent from the solution applied onto the substrate to obtain anultra-thin polymer film;

removing the textured substrate by dissolving it with a solvent thatdoes not dissolve the ultra-thin polymer film.

[9] The method according to [8] above, wherein the textured substrate isa substrate having a polymer thin film having dispersed and fixedmicroparticles, and wherein the solvent is removed from the solutionapplied onto the substrate to obtain an ultra-thin polymer film and thenthe substrate having the polymer thin film with the dispersed and fixedmicroparticles is removed by dissolving it in a solvent that does notdissolve the ultra-thin polymer film to obtain a porous ultra-thinpolymer film.[10] The method according to [9] above, wherein the microparticles areat least one type of particles selected from the group consisting ofpolystyrene particles, silica particles, dextran particles, polylacticacid particles, polyurethane microparticles, polyacrylic particles,polyethyleneimine particles, albumin particles, agarose particles, ironoxide particles, titanium oxide microparticles, alumina microparticles,talc microparticles, kaolin microparticles, montmorillonitemicroparticles and hydroxyapatite microparticles.[11] The method according to either one of [9] and [10] above whereinthe microparticles have a diameter of 20 nm-3000 nm.[12] A method for producing a porous ultra-thin polymer film comprisingthe steps of:

dissolving a polymer in a solvent to obtain a solution;

dispersing microparticles in the solution to obtain a dispersion;

applying the dispersion onto a substrate and then removing the solventfrom the dispersion applied onto the substrate to obtain an ultra-thinpolymer film; and

immersing the resulting ultra-thin polymer film in a solvent that iscapable of dissolving the microparticles to remove the microparticles,thereby obtaining a free-standing porous ultra-thin polymer film with afilm thickness of 10 nm-1000 nm.

[13] The method according to [12] above, wherein the microparticles areat least one type selected from the group consisting of inorganic salts,silica, talc, kaolin, montmorillonite, polymers, metal oxides andmetals.

[14] A method for producing a porous ultra-thin polymer film comprisingthe steps of: heating an ultra-thin polymer film built on a substrate toa glass-transition temperature or higher; and then compressing theultra-thin polymer film with a separately prepared textured substrate,thereby obtaining a free-standing porous ultra-thin polymer film with afilm thickness of 10 nm-1000 nm.[15] A method for producing a porous ultra-thin polymer film comprisingthe steps of: dissolving a polymer as a raw material to obtain asolution; dispersing microbubbles in the resulting solution; applyingthe microbubble-dispersed solution onto a substrate; and removing thesolvent from the solution applied onto the substrate, thereby obtaininga free-standing porous ultra-thin polymer film with a film thickness of10 nm-1000 nm.[16] A complex of a substrate, a water-soluble sacrificial film and aporous ultra-thin polymer film, comprising the water-soluble sacrificialfilm on the substrate, and the porous ultra-thin polymer film accordingto any one of [1], [2], [3], [4] and [5] above thereon.[16a] A complex of a substrate, a water-soluble sacrificial film and aporous ultra-thin polymer film, comprising the water-soluble sacrificialfilm on the substrate, and the porous ultra-thin polymer film accordingto any one of [2a], [2b], [3a], [4a] and [5a] above thereon.[17] A complex of a substrate, a porous ultra-thin polymer film and awater-soluble support membrane, comprising the porous ultra-thin polymerfilm according to any one of[1], [2], [3], [4] and [5] above on the substrate, and further thewater-soluble support membrane on the porous ultra-thin polymer film.[17a] A complex of a substrate, a porous ultra-thin polymer film and awater-soluble support membrane, comprising the porous ultra-thin polymerfilm according to any one of[2a], [2b], [3a], [4a] and [5a] above on the substrate, and thewater-soluble support membrane on the porous ultra-thin polymer film.[18] A complex of a porous ultra-thin polymer film and a water-solublesupport membrane, comprising the water-soluble support membrane on theporous ultra-thin polymer film according to any one of [1], [2], [3],[4] and [5] above.[18a] A complex of a porous ultra-thin polymer film and a water-solublesupport membrane, comprising the water-soluble support membrane on theporous ultra-thin polymer film according to any one of [2a], [2b], [3a],[4a] and [5a] above.[19] A method for producing a free-standing porous ultra-thin polymerfilm comprising the step of removing the water-soluble sacrificial filmor the water-soluble support membrane of the complex according to anyone of [16], [17] and [18] above with water to obtain a porousultra-thin polymer film in water.[19a] A method for producing a free-standing porous ultra-thin polymerfilm comprising a step of removing the water-soluble sacrificial film orthe water-soluble support membrane of the complex according to any oneof [16a], [17a] and [18a] above with water to obtain a porous ultra-thinpolymer film in water.[20] The method for producing the porous ultra-thin polymer filmaccording to [19] above, comprising the steps of: picking up and placingthe porous ultra-thin polymer film on another substrate; and removingwater from the picked up porous ultra-thin polymer film to obtain aporous ultra-thin polymer film in a dry state.[20a] The method for producing the porous ultra-thin polymer filmaccording to [19a] above, comprising the steps of: picking up andplacing the porous ultra-thin polymer film on another substrate; andremoving water from the picked up porous ultra-thin polymer film toobtain a porous ultra-thin polymer film in a dry state.[21] A complex of a mesh and a porous ultra-thin polymer film,comprising the porous ultra-thin polymer film according to any one of[1], [2], [3], [4] and [5] above on the mesh.[21a] A complex of a mesh and a porous ultra-thin polymer film,comprising the porous ultra-thin polymer film according to any one of[2a], [2b], [3a], [4a] and [5a] above on the mesh.[22] A method for producing a complex of a mesh and a porous ultra-thinpolymer film, comprising a step of picking up a free-standing porousultra-thin polymer film produced by the method according to [19] abovewith the mesh to produce a complex of the porous ultra-thin polymer filmand the mesh.[22a] A method for producing a complex of a mesh and a porous ultra-thinpolymer film, comprising a step of picking up a free-standing porousultra-thin polymer film produced by the method according to [19a] abovewith the mesh to produce a complex of the porous ultra-thin polymer filmand the mesh.[23] A complex of a porous ultra-thin polymer film and a nonporousultra-thin polymer film, comprising one or more porous ultra-thinpolymer films according to any one of [1],[2], [3], [4] and [5] above and one or more nonporous ultra-thin polymerfilms.[23a] A complex of a porous ultra-thin polymer film and a nonporousultra-thin polymer film, comprising one or more porous ultra-thinpolymer films according to any one of [2a], [2b], [3a], [4a] and [5a]above and one or more nonporous ultra-thin polymer films.

In addition, the present invention provides the following ultra-thinpolymer film that has been phase-separated into a sea-island structure.

[A1] An ultra-thin polymer film that has been phase-separated into asea-island structure obtained, on a substrate, by: dissolving two typesof mutually-immiscible polymers, namely, a first polymer and a secondpolymer, in a solvent in an arbitrary proportion to obtain a solution;applying the resulting solution onto the substrate; and then removingthe solvent from the solution applied onto the substrate. Here, the“first polymer” refers to a polymer that forms the island parts uponphase separation into the sea-island structure while the “secondpolymer” refers to a polymer that forms parts other than the islandparts (sea parts).[A2] The ultra-thin polymer film according to [A1] above, wherein theisland parts of the sea-island structure have a size in a range that islarger than 1 μm and smaller or equal to 25 μm, and are present on thesurface at a density of 5×10⁻³ pores/μm²-50 pores/μm².[A3] The ultra-thin polymer film according to [A2] above, wherein thesize of the pores is in a range that is smaller or equal to 15 μm.[A4] The ultra-thin polymer film according to any one of [A1]-[A3]above, wherein the film thickness of the ultra-thin polymer film is 10nm-1000 nm.[A5] The ultra-thin polymer film according to any one of [A1]-[A4]above, wherein the combination of the first and second polymers isselected from the group below:

(i) first polymer: polystyrene, and second polymer: polymethylmethacrylate;

(ii) first polymer: polystyrene, and second polymer: poly-D/L-lacticacid;

(iii) first polymer: polymethyl methacrylate, and second polymer:polystyrene;

(iv) first polymer: polyethylene glycol, and second polymer:polystyrene;

(v) first polymer: polyvinylpyrrolidone, and second polymer:polystyrene; and

(vi) first polymer: poly-D/L-lactic acid, and second polymer:polystyrene.

The present invention also provides the following substantiallydisk-like ultra-thin polymer film (herein, sometimes referred to as a“nanodisc”) and a method for producing the same.

[B1] A substantially disk-like ultra-thin polymer film whose filmthickness is 10 nm-1000 nm and whose size is in a range of 30 nm-50 μm.

[B2] The substantially disk-like ultra-thin polymer film according to[B1] above, wherein the size is in a range that is larger than 1 μm andsmaller or equal to 25 μm.

[B3] The substantially disk-like ultra-thin polymer film according to[B2] above, wherein the size is in a range that is smaller or equal to15 μm.

[B4] The substantially disk-like ultra-thin polymer film according toany one of [B1]-[B3] above, wherein the polymer is poly-D/L-lactic acid.

[C1] A method for producing a substantially disk-like ultra-thin polymerfilm comprising the steps of:

dissolving two types of mutually-immiscible polymers in a first solventin an arbitrary proportion to obtain a solution;

applying the resulting solution onto a substrate and then removing thefirst solvent from the solution applied onto the substrate to obtain anultra-thin polymer film that has been phase-separated into a sea-islandstructure; and

immersing the ultra-thin polymer film in a second solvent which is agood solvent for the polymer of the sea parts but a poor solvent for thepolymer other than the sea parts to remove the sea parts, therebyobtaining a substantially disk-like ultra-thin polymer film with a filmthickness of 10 nm-1000 nm and a size in a range of 30 nm-50 nm.

Effect of the Invention

The present invention is capable of providing a free-standing porousultra-thin polymer film and a method for producing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 AFM images of PS/PMMA blend nanosheets that were prepared at arotation speed of 5000 rpm. Images after the film formation (top row),the top surfaces after the treatment with the solvent (middle row), andthe back surfaces after the treatment with the solvent (bottom row).PS:PMMA (w/w) were 0:10 (left column), 1:9 (second column), 2:8 (thirdcolumn) and 3:7 (fourth column).

FIG. 2 AFM images of PS/PMMA blend nanosheets that were prepared withPS:PMMA (w/w) in 2:8. Images after the film formation (top row), the topsurfaces after the treatment with the solvent (middle row), and the backsurfaces after the treatment with the solvent (bottom row). Rotationspeeds (rpm) were 1000 (left column), 3000 (second column), 5000 (thirdcolumn) and 7000 (fourth column).

FIG. 3 SEM images of porous nanosheets obtained under the respectivepreparation conditions. (a) 1:9 w/w, 1000 rpm (cross-section); (b) 1:9w/w, 5000 rpm (cross-section); (c) 2:8 w/w, 1000 rpm (cross-section);(d) 2:8 w/w, 5000 rpm (perspective images of the top surface); and (e)2:8 w/w, 3000 rpm (perspective images of the top surface).

FIG. 4 AFM images of PS/D,L-PLA blend nanosheets prepared withPS:D,L-PLA (w/w) in 3:7. Images after the film formation (top row) andthe surfaces after the treatment with the solvent (bottom row). Rotationspeeds (rpm) were 1000 (left column), 3000 (second column), 5000 (thirdcolumn) and 7000 (fourth column).

FIG. 5 AFM images of D,L-PLA porous nanosheets obtained by a methodusing a mixed solvent. The top and the rear surfaces with ethylacetate:DMSO (v/v) in 100:1 (top and second rows), the top and the rearsurfaces with ethyl acetate:DMSO (v/v) in 100:3 (third and fourth rows),and the top and the rear surfaces with ethyl acetate: DMSO (v/v) in100:5 (fifth and sixth rows). Rotation speeds (rpm) were 1000 (leftcolumn), 3000 (middle column) and 5000 (right column).

FIG. 6 AFM images of D,L-PLA nanosheets having PS microparticles appliedonto textured substrates. The PS microparticle-fixed PVA films preparedat respective rotation speeds (top row), the films obtained bycompositing D,L-PLA nanosheets with the respective PVA films (secondrow), and the top surface (third row) and the rear surface (fourth row)of the porous D,L-PLA nanosheets after treating them through immersionin water. The rotation speeds (rpm) were 1000 (left column), 2000(second column), 3000 (third column) and 5000 (fourth column).

FIG. 7 AFM images of D,L-PLA porous nanosheets obtained by a method thatuses microparticles (precipitation/crystallization technique).D,L-PLA:LiBr (w/w) in 5:1 (top row), D,L-PLA:LiBr (w/w) in 5:2 (secondrow), D,L-PLA:LiBr (w/w) in 5:3 (third row), D,L-PLA:LiBr (w/w) in 5:4(fourth row) and D,L-PLA:LiBr (w/w) in 5:5 (fifth row). Images after thefilm formation (left column), the top surfaces after treating themthrough immersion in water (second column), and enlarged regions shownas AFM images in the third and fourth columns. Each of the rotationspeeds (rpm) was 3000.

FIG. 8 Schematic cross-sectional views of a porous ultra-thin polymerfilm and respective complexes. (a) A porous ultra-thin polymer film 1,(b) a complex 4 of a substrate 3, a water-soluble sacrificial film 2 andthe ultra-thin polymer film 1, (c) a complex 6 of a substrate 3, theporous ultra-thin polymer film 1 and a water-soluble support membrane 5,(d) a complex 7 of the porous ultra-thin polymer film 1 and awater-soluble support membrane 5, (e) a complex 9 of a mesh 8 and theporous ultra-thin polymer film 1, and (I) a complex 11 of the porousultra-thin polymer film 1 and a nonporous ultra-thin film 10.

FIG. 9 AFM images of PDLLA/PS nanosheets and porous PS nanosheets. AFMimages have PDLLA:PS ratios=1:9, 2:8 and 3:7 (w/w), respectively, fromthe left.

FIG. 10 AFM images of PDLLA/PS nanosheets and porous PS nanosheets. (a)an AFM image of a PDLLA/PS nanosheet, (a′) a 3D AFM image of a PDLLA/PSnanosheet, (b) an AFM image of a porous PS nanosheet, and (b′) a 3D AFMimage of a porous PS nanosheet.

FIG. 11 A schematic view of a porous PS nanosheet.

FIG. 12 AFM images of PDLLA nanodiscs. (a), (b) AFM images of monolayerPDLLA nanodiscs, and (c) an AFM image of a bilayer PDLLA nanodisc.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. Thescope of the present invention is not limited to these descriptions, andmay be carried out according to a procedure other than the followingexamples through appropriate alteration without departing from thespirit of the present invention. All of the documents and publicationscited herein are hereby incorporated by reference in their entiretyregardless of the purposes thereof. In addition, the presentspecification incorporates the disclosed content of the claims,specification and figures of Japanese Patent Application No. 2012-054255(filed on Mar. 12, 2012) based on which the present application claimspriority.

Herein, an ultra-thin film may sometimes be referred to as a“nanosheet”.

1. Porous Ultra-Thin Polymer Film of the Present Invention

FIG. 8(a) shows one example of a porous ultra-thin polymer film 1 of thepresent invention.

A porous ultra-thin polymer film of the present invention is afree-standing ultra-thin film. The term “free-standing” refers to aproperty of an ultra-thin film, which means that no support is requiredfor the ultra-thin film to maintain the film structure. This, however,does not deny that an ultra-thin film of the present invention may forma complex with a support.

The term “porous” means that a plurality of pores are provided in anultra-thin film. Moreover, the pores may or may not penetrate throughthe ultra-thin polymer film. A porous ultra-thin polymer film of thepresent invention may have penetrating pores only, non-penetrating poresonly or both of the penetrating pores and the non-penetrating pores asshown in FIG. 8(a). The form of such pores may appropriately bedetermined according to usage. A porous ultra-thin polymer film of thepresent invention may have pores formed in any kind of shapes such assubstantially disk-like, oval, rectangular, square or the like when thesurface of the film is seen from above, but in general, it issubstantially disk-like. Although not shown, substantially disk-likepores may merge with each other.

A porous ultra-thin polymer film of the present invention has a filmthickness of 10 nm-1000 nm. The film thickness of a porous ultra-thinpolymer film of the present invention may be 10 nm-1000 nm, which mayappropriately be determined according to usage, while the film thicknessis preferably 20 nm-800 nm, more preferably 30 nm-600 nm, still morepreferably 40 nm-400 nm, and particularly preferably 50 nm-200 nm.

A porous ultra-thin polymer film of the present invention has aplurality of pores in the surface. Herein, the term “surface” refers tothe top or the back surface of an ultra-thin film. The pore density ofthe surface may be any density as long as there are a plurality ofpores, and the pore density of the surface may appropriately bedetermined according to usage thereof, while the pore density of thesurface (pores/μm²) is generally 0.005 pores/μm²-100 pores/μm²,preferably 0.05 pores/m²-50 pores/μm², more preferably 0.1 pores/μm²-30pores/μm², and still more preferably 0.5 pores/μm²-20 pores/μm².

In the case where the pores are substantially disk-like, the porediameter is not particularly limited and may appropriately be determinedaccording to usage thereof, while the pore diameter is preferably 0.01μm-500 μm, more preferably 0.03 μm-100 μm, still more preferably 0.1μm-5 μm, and particularly preferably 0.5 μm-3 μm.

Alternatively, the pore diameter is in a range that is larger than 1 μmand smaller or equal to 25 μm, more preferably in a range that is largerthan 1 μm and smaller or equal to 20 μm, still more preferably in arange that is larger than 1 μm and smaller or equal to 18 μm, andparticularly preferably in a range that is larger than 1 μm and smalleror equal to 15 μm.

A plurality of pores with the same or different pore diameters may beprovided in a single ultra-thin film.

When a plurality of pores with different pore diameters are provided,the pore diameter distribution may, for example, be ±10% or more. Insome embodiments of the present invention, the pore diameterdistribution is ±20% or more, preferably ±25% or more, more preferably±30% or more, and still more preferably ±35% or more (for example, ±35%or more, ±40% or more, ±45% or more or ±50% or more). Furthermore, insome embodiments of the present invention, the pore diameterdistribution ranges from the above-mentioned lower limit ±10% or moreto, for example, ±200% or less, ±150% or less, ±100% or less, ±50% orless, ±40% or less, ±30% or less, ±20% or less or ±15% or less.

In some other embodiments of the present invention, the pore diameterdistribution ranges from the above-mentioned lower limit ±20% or more(for example, ±20% or more, ±25% or more, ±30% or more, ±35% or more,±40% or more, ±45% or more or ±50% or more) to ±200% or less or ±150% orless.

Herein, the term “pore diameter distribution” refers to a valuecalculated as follows. Briefly, a pore diameter distribution iscalculated as σ/μ by approximating the distributions of the porediameters to give the normal distribution, where the mean is μ and thedeviation is σ².

On the other hand, when a plurality of pores with different porediameters are provided, the pore diameter difference between the porewith the maximum pore diameter and the pore with the minimum porediameter is generally 0.01 μm-500 μm, preferably 0.03 μm-100 μm, stillmore preferably 0.1 μm-5 μm, and particularly preferably 0.5 μm-3 μm.

In a preferable embodiment of a porous ultra-thin film of the presentinvention, the ratio of a pore diameter to a film thickness of theporous ultra-thin polymer film (pore diameter (μm)/film thickness (μm))is, for example, 0.1-50, preferably 0.2-40, more preferably 0.3-20 andparticularly preferably 0.5-15.

Moreover, the pores may be provided on both of the top and the backsurfaces of the porous ultra-thin polymer film as shown in FIG. 8(a), oronly on one of the surfaces (only on the top surface or only on the backsurface). When the pores are provided on both of the top and the backsurfaces of the porous ultra-thin polymer film, the pore density may bethe same or different between the top and back surfaces. The arrangementof such pores may appropriately be determined according to usage.

A porous ultra-thin polymer film of the present invention may have anysize and any shape. The size is 0.05 mm-50 cm, preferably 0.1 min-10 cm,and more preferably 0.3 mm-5 cm. The shape is not particularly limitedbut it may be, for example, a flat shape such as a circle, an oval, asquare, a hexagon, a ribbon shape, a string shape, a multibranched shapeor a star shape, or a three-dimensional shape such as a tube, a convex,a shape of a face mask or a shape of a handprint. The shape of a porousultra-thin polymer film may appropriately be determined according tousage.

A polymer composing a porous ultra-thin polymer film of the presentinvention is not particularly limited and may appropriately be selectedaccording to usage. A polymer used for composing a porous ultra-thinpolymer film of the present invention may be a polymer that isdescribed, for example, in the following documents: Yasuhiko TABATA ed.,“Biomaterial for Regenerative Medicine”, Corona Publishing; SadaoANAZAWA ed., “Dressing: New Wound Management”, Herusu Shuppan; JapaneseSociety for Biomaterials ed., “Basis of Biomaterials”; Journal ofBiomaterials, “Biomaterials utilized by making contact with blood”(feature article), Biomaterials, 22, 78-139 (2004), “Biomaterialsutilized by making contact with blood (second series)” (featurearticle), Biomaterials, 23, 178-238 (2005); and “Biomedical Applicationsof Biodegradable Polymers”, Journal of Polymer Science, Part B: PolymerPhysics, 49, 832-864 (2011).

Preferably, a polymer composing a porous ultra-thin polymer film of thepresent invention is at least one selected from the group consisting of:

(i) polyhydroxyalkanoic acid such as poly-D,L-lactic acid, polyglycolicacid, hydroxybutyric acid or polycaprolactone;

(ii) a copolymer such as a copolymer of lactic acid and glycolic acid, acopolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid, acopolymer of trimethylene carbonate and glycolide, or a copolymer ofpolyglycolic acid and poly-ε-caprolactone;

(iii) poly(ester-ether) such as polydioxane orpoly(2-methylene-1,3,6-trioxocane);

(iv) a polyester of aliphatic dicarboxylic acid and aliphatic diol, suchas polybutylene succinate, polyethylene adipate or polyethylenesuccinate;

(v) polyamides such as polyesteramide, polyamide 4, polyaspartic esteror polyglutamic ester or polyurethane;

(vi) a polysaccharide such as acetylcellulose, polyglucuronic acid,alginic acid or chitosan, or polysaccharide ester;

(vii) poly(acrylate) such as polymethyl acrylate, polyethyl acrylate orpolybutyl acrylate;

(viii) poly(methacrylate) such as polymethyl methacrylate, polyethylmethacrylate, polycaprylyl methacrylate, polyglyceryl methacrylate,polyglucosylethyl methacrylate, polybutyl methacrylate, polypropylmethacrylate or polymethacryloyloxy ethyl phosphorylcholine;

(ix) polystyrene or polyvinyl acetate; and

(x) polysiloxane such as polydimethyl siloxane;

In some embodiments of the present invention, a polymer ispoly(methacrylate), preferably polymethyl methacrylate, polyethylmethacrylate or polypropyl methacrylate, and more preferably polymethylmethacrylate.

In some other embodiments of the present invention, a polymer ispolyhydroxyalkanoic acid or a copolymer of polyhydroxyalkanoic acid,preferably poly-D,L-lactic acid, polyglycolic acid or a copolymer oflactic acid and glycolic acid, and more preferably poly-D,L-lactic acid.

A preferred embodiment of a porous ultra-thin polymer film of thepresent invention may be used, for example, as a cell culture support, anano/microfilter, a highly light-scattering film, a cell isolationfilter or the like.

The phrase “use of a porous ultra-thin polymer film as a cell support”means that it is used as a scaffolding member that allows a substance topass therethrough, and specifically refers to a case where a porousultra-thin polymer film is used as follows. It is used as a scaffoldupon culturing cells from a stem cell to form a tissue such as skin,cornea, cardiac muscle, nerve or the like. The cells are cultured in apetri dish but efficient supply of oxygen, nutrients or the like orexcretion of waste products cannot be provided from the substrate side.Therefore, there is a concern that the resulting cellular tissue mayhave different property from that of the original cellular tissue.Moreover, there is a limit to multi-layering since when the cell layersof a cultured tissue are simply laminated, passing of oxygen, nutrients,waste products or the like become difficult. Hence, a porous ultra-thinpolymer film can be used as a scaffolding member that allows passing ofa substance.

When a porous ultra-thin polymer film is used as a cell culture support,the polymer of the film is preferably polyhydroxyalkanoic acid such aspoly-D,L-lactic acid, polyglycolic acid, hydroxybutyric acid orpolycaprolactone, a copolymer such as a copolymer of lactic acid andglycolic acid, a copolymer of 3-hydroxybutyric acid and 3-hydroxyvalericacid, a copolymer of trimethylene carbonate and glycolide or a copolymerof polyglycolic acid and poly-ε-caprolactone, poly(ester-ether) such aspolydioxane or poly(2-methylene-1,3,6-trioxocane), or a polyester ofaliphatic dicarboxylic acid and aliphatic diol, such as polybutylenesuccinate, polyethylene adipate or polyethylene succinate, and morepreferably polyhydroxyalkanoic acid such as poly-D,L-lactic acid,polyglycolic acid, hydroxybutyric acid or polycaprolactone, or acopolymer such as a copolymer of lactic acid and glycolic acid, acopolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid, acopolymer of trimethylene carbonate and glycolide or a copolymer ofpolyglycolic acid and poly-ε-caprolactone.

When a porous ultra-thin polymer film is used as a cell culture support,the film thickness is preferably 30 nm-1000 nm, more preferably 50nm-1000 nm, still more preferably 100 nm-1000 nm, and particularlypreferably 200 nm-1000 nm.

When a porous ultra-thin polymer film is used as a cell support, thepore density (pores/μm²) of the surface of the film is generally 0.005pores/μm²-100 pores/μm², preferably 0.05 pores/μm²-50 pores/μm², morepreferably 0.1 pores/μm²-30 pores/μm², and still more preferably 0.5pores/μm²-20 pores/μm².

When it is used as a cell culture support, an appropriate pore diameteris such that it does not allow cells of interest to penetratetherethrough but allow them to adsorb thereto, which is preferably 0.01μm-50 μm, more preferably 0.03 μm-10 μm, still more preferably 0.1 μm-5μm, and particularly preferably 0.5 μm-3 μm.

Furthermore, when a porous ultra-thin polymer film is used as a cellculture support, pores are preferably provided on both top and backsurfaces of the film while the pore density may be the same or differentbetween the top surface and the back surface.

Additionally, a porous ultra-thin polymer film preferably only haspenetrating pores but it may have both penetrating pores andnon-penetrating pores. Preferably, the shape of the porous ultra-thinpolymer film is substantially disk-like, oval or the like.

The phrase “a porous ultra-thin polymer film is used as anano/microfilter” specifically means that the porous ultra-thin polymerfilm is used as follows. Specifically, a porous ultra-thin film isplaced on a coarse support for the purpose of controlling passing ofvarious polymers, proteins, viruses or particles. It may be used, forexample, as a virus removing film or a protein removing film.

When a porous ultra-thin polymer film is used as a nano/microfilter, thepolymer of the film is poly(methacrylate), preferably polymethylmethacrylate, polyethyl methacrylate, or polypropyl methacrylate, andmore preferably polymethyl methacrylate. When a porous ultra-thinpolymer film is used as a nano/microfilter, the film thickness is 30nm-1000 nm, more preferably 50 nm-1000 nm, still more preferably 100nm-1000 nm, and particularly preferably 200 nm-1000 nm.

When a porous ultra-thin polymer film is used as a nano/microfilter, thepore density (pores/μm²) of the surface of the film is made as high aspossible but in a fit state to maintain the film strength. In general,the pore density is 0.01 pores/μm²-100 pores/μm², preferably 0.05pores/μm²-100 pores/μm², more preferably 0.1 pores/μm²-100 pores/μm²,and still more preferably 1 pore/μm²-100 pores/μm².

When a film is used as a nano/microfilter, the pore diameter should beappropriate for blocking a substance or particles of interest, which ispreferably 0.001 μm-50 μm, and more preferably 0.01 μm-10 μm.

In addition, when a porous ultra-thin polymer film is used as anano/microfilter, the pores are preferably provided on both top and backsurfaces of the film while the pore densities may be the same ordifferent between the top and back surfaces. The porous ultra-thinpolymer film preferably only has penetrating pores but it may also haveboth penetrating pores and non-penetrating pores. In addition, the porediameter distribution is preferably as narrow as possible. Specifically,the pore diameter distribution lies, for example, in a range of ±10% to±40%, preferably in a range of ±10% to ±30%, more preferably in a rangeof +10% to ±20%, and still more preferably in a range of ±10% to ±15%.

Preferably, the shape of the porous ultra-thin polymer film issubstantially disk-like, square or the like.

Alternatively, application to cell culture and use as a filter may becombined, in which case the film may be made, for example, into asac-like shape or a pipe-like shape to be used for the purpose ofculturing floating cells or blood cells therein and sorting themaccording to size.

The phrase “a porous ultra-thin polymer film is used as a highlylight-scattering film” specifically means that the porous ultra-thinpolymer film is used as follows. The porous ultra-thin polymer film ofthe present invention have a plurality of pores capable of scatteringlight. Such a highly light-scattering film can be used by being appliedonto an application subject. The application subject may, for example,be a surface of a tissue outside an organism (skin, nail, hair, etc.), asurface of a tissue inside an organism (for example, internal organ,blood vessel, tumor, etc.) or the like.

Some embodiments of a porous ultra-thin polymer film of the presentinvention may be used by being applied onto skin for the purpose ofconcealing spots, bruise, moles or wrinkle of the skin.

Some of other embodiments of a porous ultra-thin polymer film of thepresent invention may be used by being applied onto a surface of aninternal organ for the purpose of marking upon abdominal section orendoscopic surgery.

Some of further embodiments of a porous ultra-thin polymer film of thepresent invention may be used by being applied onto skin, nail or hairfor the purpose of body painting, nail art or hair coloring.

Preferably, the porous ultra-thin polymer film of the present inventionmay be used by being applied onto skin for the purpose of concealingspots, bruise, moles or wrinkle of the skin.

When a porous ultra-thin polymer film is used as a highlylight-scattering film, the shape and size of the film are selected suchthat they are appropriate for accomplishing the purpose thereof while itis preferably disk-like, polygonal, tape-like or the like.Alternatively, a dispersion of fine highly light-scattering films may beprepared to be used for spray atomization or as cream.

When a porous ultra-thin polymer film is used as a highlylight-scattering film, the polymer of the film is preferablypolyhydroxyalkanoic acid such as poly-D,L-lactic acid, polyglycolicacid, hydroxybutyric acid or polycaprolactone, a copolymer such as acopolymer of lactic acid and glycolic acid, a copolymer of3-hydroxybutyric acid and 3-hydroxyvaleric acid, a copolymer oftrimethylene carbonate and glycolide or a copolymer of polyglycolic acidand poly-ε-caprolactone, poly(ester-ether) such as polydioxane orpoly(2-methylene-1,3,6-trioxocane), or a polyester of aliphaticdicarboxylic acid and aliphatic diol, such as polybutylene succinate,polyethylene adipate or polyethylene succinate, and more preferablypolyhydroxyalkanoic acid such as poly-D,L-lactic acid, polyglycolicacid, hydroxybutyric acid or polycaprolactone, or a copolymer such as acopolymer of lactic acid and glycolic acid, a copolymer of3-hydroxybutyric acid and 3-hydroxyvaleric acid, a copolymer oftrimethylene carbonate and glycolide or a copolymer of polyglycolic acidand poly-ε-caprolactone.

When a porous ultra-thin polymer film is used as a highlylight-scattering film, the film thickness of the film is selected whileplacing emphasis on adherence onto an application subject (for example,skin), which is preferably 20 nm-900 nm, more preferably 30 nm-500 nm,still more preferably 40 nm-300 nm, and particularly preferably 50nm-200 nm.

When a porous ultra-thin polymer film is used as a highlylight-scattering film, the pore density (pores/μm²) of the surface ofthe film is generally 0.01 pores/μm²-100 pores/μm², preferably 0.05pores/μm²-80 pores/μm², more preferably 0.1 pores/μm²-50 pares/μm², andstill more preferably 1 pore/μm²-30 pores/μm².

When it is used as a highly light-scattering film, the pore diametershould be appropriate for efficiently scatting light in a broadwavelength range in random directions, which is preferably 0.01 μm-50μm, more preferably 0.03 μm-10 μm, and still more preferably 0.1 μm-5μm. Although a single ultra-thin film may be provided with a pluralityof pores having the same or different pore diameters, a plurality ofpores with different pore diameters are preferable. When a plurality ofpores with different pore diameters are provided, the difference in thepore diameters between the pore with the maximum pore diameter and thepore with the minimum pore diameter is generally 0.01 μm-500 preferably0.03 μm-100 μm, still more preferably 0.1 μm-5 μm, and particularlypreferably 0.5 μm-3 μm. The distribution of the pores is preferably aslarge as possible so as to obtain random light scattering, which isspecifically a pore diameter distribution, for example, in a range of±20% to ±200%, preferably in a range of ±30% to +200%, more preferablyin a range of ±50% to ±150%, and still more preferably in a range of+50% to ±100%.

Furthermore, the pores are preferably provided on both of the top andback surfaces of the porous ultra-thin polymer film while the poredensities may be the same or different between the top and backsurfaces. Moreover, although the porous ultra-thin polymer filmpreferably has only penetrating pores, it may have both of thepenetrating pores and the non-penetrating pores.

The phrase “use of a porous ultra-thin polymer film as a cell isolationfilter” specifically means that the porous ultra-thin polymer film isused as follows. Specifically, a porous ultra-thin film is applied ontoa coarse support for the purpose of controlling the passing of variouscells.

When a porous ultra-thin polymer film is used as a cell isolationfilter, the polymer of the film is poly(methacrylate), preferablypolymethyl methacrylate, polyethyl methacrylate or polypropylmethacrylate, and more preferably polymethyl methacrylate. When a porousultra-thin polymer film is used as a cell isolation filter, the filmthickness of the film is 30 nm-1000 nm, more preferably 50 nm-1000 nm,still more preferably 100 nm-1000 nm, and particularly preferably 200nm-1000 nm.

When a porous ultra-thin polymer film is used as a cell isolationfilter, the pore density (pores/μm²) of the surface of the film is madeas high as possible but in a fit state to maintain the film strength.The pore density is generally 0.01 pores/μm²-100 pores/μm², preferably0.05 pores/μm²-100 pores/μm², more preferably 0.1 pores/μm²-100pores/μm², and still more preferably 1 pore/μm²-100 pores/μm².

When the film is used as a cell isolation filter, the pore diametershould be appropriate for blocking the passing of a cell of interest,which lies preferably in a range that is larger than 1 μm and smaller orequal to 25 μm, more preferably in a range that is larger than 1 μm andsmaller or equal to 20 μm, more preferably in a range that is largerthan 1 μm and smaller or equal to 18 μm, and particularly preferably ina range that is larger than 1 μm and smaller or equal to 15 μm.

When a porous ultra-thin polymer film is used as a cell isolationfilter, the pores are preferably provided on both of the top and theback surfaces of the film while the pore densities may be the same ordifferent between the top and the back surfaces. Moreover, although theporous ultra-thin polymer film preferably has only penetrating pores, itmay have both of the penetrating pores and the non-penetrating pores. Inaddition, the pore diameter distribution is preferably as narrow aspossible. Specifically, the pore diameter distribution lies, forexample, in a range of ±10% to ±40%, preferably in a range of ±10% to±30%, more preferably in a range of ±10% to ±20%, and still morepreferably in a range of ±10% to ±15%.

Preferably, the shape of the porous ultra-thin polymer film issubstantially disk-like, square or the like.

2. Complex of Substrate, Water-Soluble Sacrificial Film and PorousUltra-Thin Polymer Film, and Complex of Substrate, Ultra-Thin PolymerFilm and Water-Soluble Support Membrane

A porous ultra-thin polymer film of the present invention may form acomplex together with a substrate and a water-soluble sacrificial film.Such a complex is shown in FIG. 8(b) as a complex 4 comprising asubstrate, a water-soluble sacrificial film and a porous ultra-thinpolymer film, wherein the complex has the water-soluble sacrificial film2 on the substrate 3, and the porous ultra-thin polymer film 1 of thepresent invention further thereon.

Alternatively, a porous ultra-thin polymer film of the present inventionmay form a complex together with a substrate and a water-soluble supportmembrane. Such a complex is shown in FIG. 8(c) as a complex 6 comprisinga substrate, a porous ultra-thin polymer film and a water-solublesupport membrane, wherein the complex has the porous ultra-thin polymerfilm 1 of the present invention on the substrate 3, and thewater-soluble support membrane 5 further thereon.

The substrate is not particularly limited as long as it can support theporous ultra-thin polymer film, and it is generally a silicon substrate,a glass substrate, a metal substrate, polyester, polypropylene,polyethylene, polyvinyl chloride, polystyrene, polyacrylonitrile,polycarbonate, an ethylene vinyl acetate copolymer, an ethylene-vinylalcohol copolymer, an ethylene-methacrylic acid copolymer, or a filmsuch as a nylon film, preferably a silicon substrate, polyester,polypropylene, polyethylene or the like, and more preferably a siliconsubstrate, polyester or the like.

The film thickness of the substrate is generally 1 μm-5000 μm,preferably 5 μm-1000 μm, more preferably 10 μm-500 μm, still morepreferably 30 μm-300 μm, and particularly preferably 50 μm-100 μm.

The porous ultra-thin polymer film of the present invention is asdescribed above.

The water-soluble sacrificial film or the water-soluble support membraneis not particularly limited as long as it can be dissolved with water,and it is generally a polyvinyl alcohol film, a polyacrylate film, apolymethacrylate film, a sodium alginate film, a polyethylene oxidefilm, a polyacrylic amide film, a polyvinylpyrrolidone film, a starchfilm, a carboxymethyl cellulose film, a collagen film, a pullulan film,an agar film, a silicon film or the like, preferably a polyvinyl alcoholfilm, a polyacrylate film, a starch film, a collagen film, an agar filmor the like, more preferably a polyvinyl alcohol film, a starch film, acollagen film or the like, and still more preferably a polyvinyl alcoholfilm.

The film thickness of the water-soluble sacrificial film is generally 5nm-1000 nm, preferably 5 nm-500 nm, more preferably 10 nm-300 nm, stillmore preferably 10 nm-200 nm, and particularly preferably 10 nm-100 nm.

The film thickness of the water-soluble support membrane is generally 50nm-20000 nm, preferably 100 nm-10000 nm, more preferably 200 nm-5000 nm,still more preferably 500 nm-5000 nm, and particularly preferably 700nm-5000 nm.

3. Complex of Porous Ultra-Thin Polymer Film and Water-Soluble SupportMembrane

A porous ultra-thin polymer film of the present invention may form acomplex together with a water-soluble support membrane.

Such a complex is shown in FIG. 8(d) as a complex 7 of a porousultra-thin polymer film and a water-soluble support membrane, whereinthe complex has the water-soluble support membrane 5 on the porousultra-thin polymer film 1 of the present invention.

When this complex is immersed in water, the water-soluble supportmembrane is dissolved, thereby obtaining a porous ultra-thin polymerfilm. The resulting porous ultra-thin polymer film is free-standing.Herein, the term “free-standing” refers to a form where the porousultra-thin polymer film independently exists without a support.

The porous ultra-thin polymer film and the water-soluble supportmembrane of the present invention are as described above.

For example, the complex of the porous ultra-thin polymer film and thewater-soluble support membrane can be applied onto an applicationsubject, which is then washed with water to remove the water-solublesupport membrane, thereby applying the porous ultra-thin polymer filmonto the application subject.

4. Complex of Mesh and Porous Ultra-Thin Polymer Film

A porous ultra-thin polymer film of the present invention may form acomplex together with a mesh.

Such a complex is shown in FIG. 8(e) as a complex 9 of a mesh and aporous ultra-thin polymer film, wherein the complex has the porousultra-thin polymer film 1 of the present invention on the mesh 8.

The porous ultra-thin polymer film of the present invention is asdescribed above.

The mesh may be anything as long as it is capable of supporting theporous ultra-thin polymer film of the present invention and capable ofbeing easily peeled off from the porous ultra-thin polymer film uponapplication. Examples of the mesh include meshes formed from thoseselected from the group consisting of nylon, polyester, Teflon(registered trademark), polypropylene, silk and the like. The size ofthe mesh is generally 1-4000 μm, preferably 5-400 μm, more preferably10-200 μm, and particularly preferably 40-100 μm.

The film thickness of the mesh is generally 5 μm-1000 μm, preferably 7μm-700 μm, more preferably 10 μm-500 μm, still more preferably 30 μm-300μm, and particularly preferably 50 μm-100 μm.

For example, the complex of the mesh and the porous ultra-thin polymerfilm is applied onto an application subject and then the mesh is peeledoff from the porous ultra-thin polymer film, thereby easily applying theporous ultra-thin polymer film onto the application subject.

5. Complex of Porous Ultra-Thin Polymer Film and Nonporous Ultra-ThinFilm

A porous ultra-thin polymer film of the present invention may form acomplex together with a nonporous ultra-thin film. The term “nonporous”means that an ultra-thin film is not provided with the pores like thoseprovided in the above-described porous ultra-thin polymer film.

This complex is shown in FIG. 8(f) as a complex 11 of a porousultra-thin polymer film and a nonporous ultra-thin film, wherein thecomplex has the porous ultra-thin polymer film 1 of the presentinvention on the nonporous ultra-thin film 10.

The number of the porous ultra-thin polymer film in the complex may beone or more (for example, 1-20 layers, 1-10 layers or 1-5 layers) whilethe number of the nonporous ultra-thin film may also be one or more (forexample, 1-20 layers, 1-10 layers or 1-5 layers).

The laminated order of the porous ultra-thin polymer film and thenonporous ultra-thin film in the complex is not particularly limited.When the complex comprises three or more layers, the porous ultra-thinpolymer film may be included as one or more of the layers from thebottommost layer to the uppermost layer.

When two or more porous ultra-thin polymer films are comprised in thecomplex, the film thicknesses, the pore sizes, the pore densities, thepore diameter distributions, the ratios of the pore diameters to thefilm thicknesses, the materials and the like of the ultra-thin films maybe different or all or some of them may be identical among the porousultra-thin polymer films.

When two or more nonporous ultra-thin films are comprised in thecomplex, the film thicknesses, the materials and the like of theultra-thin films may be different or all or some of them may beidentical among the ultra-thin films.

The film thickness of a nonporous ultra-thin film is generally 10nm-1000 nm, preferably 20 nm-800 nm, more preferably 30 nm-600 nm, stillmore preferably 40 nm-400 nm, and particularly preferably 50 nm-200 nm.

The material of a nonporous ultra-thin film may appropriately beselected according to usage and it is, for example, polylactic acid, acopolymer of lactic acid and glycolic acid, polyglycolic acid,polycaprolactone, silicon, dimethicone, polyvinyl acetate, carboxymethylcellulose, polyvinylpyrrolidone, collagen, an acrylic polymer such an(alkyl acrylate/diacetone acrylamide) copolymer, an (alkylacrylate/dimethicone) copolymer or a methacrylic polymer, polyurethaneor the like, and preferably polylactic acid, a copolymer of lactic acidand glycolic acid, carboxymethyl cellulose, polyurethane or acrylicpolymer.

A nonporous ultra-thin film may be produced, for example, according to amethod described, for example, in WO 2006/025592, WO2008/050913, Adv.Mater. 2009, 21, 4388-4392 or the like or a method pursuant thereto.

A complex of a porous ultra-thin polymer film and a nonporous ultra-thinfilm may be produced by sequentially forming a porous ultra-thin polymerfilm (layer) and a nonporous ultra-thin film (layer) from the firstplace. Alternatively, it may be produced by adhering separately producedporous ultra-thin polymer film and nonporous ultra-thin film.

Such a complex may be used, for example, as the above-described highlylight-scattering film.

6. Method for Producing Porous Ultra-Thin Polymer Film of the PresentInvention

A porous ultra-thin polymer film of the present invention may beproduced, for example, according to the following method.

(1) Method Using Two Types of Polymers

According to this method, first, two types of mutually-immisciblepolymers are dissolved in a first solvent in an arbitrary proportion toobtain a solution.

The phrase “two types of mutually-immiscible polymers” refers to twotypes of polymers that are mutually immiscible in solid states.Hereinafter, among the two types of polymers, a polymer that forms theisland parts upon phase separation into a sea-island structure isreferred to as polymer 1, while a polymer other than the island parts isreferred to as polymer 2. Examples of combinations of such polymers mayinclude the combinations mentioned below.

The term “arbitrary proportion” means that the ratio (w/w) of polymer1:polymer 2 is arbitrary, where the ratio (w/w) of polymer 1:polymer 2may, for example, be 1:9-5:5. The ratio (w/w) of polymer 1:polymer 2 ispreferably 1:9-4:6, and more preferably 1:9-3:7.

The first solvent is not limited as long as it is capable of dissolvingthe above-mentioned two types of polymers but generally it is at leastone type of solvent selected from the group consisting ofdichloromethane, diethyl ether, methyl acetate, acetone, chloroform,methanol, tetrahydrofuran, dioxane, ethyl acetate, methyl ethyl ketone,benzene, acetonitrile, isopropyl alcohol, dimethoxyethane, ethyleneglycol monoethyl ether (also known as cellosolve), ethylene glycolmonoethyl ether acetate (also known as cellosolve acetate), ethyleneglycol mono-normal-butyl ether (also known as butyl cellosolve),ethylene glycol monomethyl ether (also known as methyl cellosolve)toluene, N,N-dimethyl formamide and dimethylacetamide. The first solventis preferably at least one type of solvent selected from the groupconsisting of dichloromethane, diethyl ether, acetone, chloroform,tetrahydrofuran, dioxane, ethyl acetate, methyl ethyl ketone,acetonitrile, isopropyl alcohol, dimethoxyethane, N,N-dimethyl formamideand dimethylacetamide, more preferably at least one type of solventselected from the group consisting of dichloromethane, acetone,tetrahydrofuran, ethyl acetate, methyl ethyl ketone, acetonitrile,isopropyl alcohol and N,N-dimethyl formamide, and more preferably atleast one type of solvent selected from the group consisting ofdichloromethane, tetrahydrofuran and ethyl acetate.

The total weight concentration of the polymer in the solution isgenerally 0.1 wt %-20 wt %, preferably 0.3 wt %-10 wt %, and morepreferably 0.5 wt %-2 wt %.

Then, the resulting solution is applied onto a substrate, and the firstsolvent is removed from the solution applied onto the substrate, therebyobtaining an ultra-thin polymer film that has been phase-separated intoa sea-island structure.

A method for applying a solution onto a substrate is not particularlylimited and a solution may be applied onto a substrate, for example, bya common technique such as a spin-coating technique, a spray coatingtechnique, a bar-coating technique, a dip coating technique or the like.Alternatively, a solution may be thinly applied onto a substrate by acommon printing technique such as gravure printing, screen printing, inkjet printing or the like.

Subsequently, the first solvent is removed from the solution appliedonto the substrate. A method for removing the first solvent is also notparticularly limited. For example, if the solution has been applied ontothe substrate by a spin-coating technique, rotation can be continued toevaporate and remove the first solvent. Alternatively, the first solventmay be evaporated and removed by heating. Alternatively, the firstsolvent may be removed by decompression. Alternatively, the firstsolvent may be removed by combining two or more of these methods forremoving the first solvent.

Subsequently, the ultra-thin polymer film that has been phase-separatedinto a sea-island structure is immersed in a second solvent which is agood solvent for polymer 1 as the island parts but a poor solvent forpolymer 2 other than the island parts to remove the island parts,thereby obtaining a porous ultra-thin polymer film.

A combination of polymer 1, polymer 2 and the second solvent may bebased on the calculation of the dissolution parameters according to amethod described, for example, in the document, “SP Values, Basis,Applications and Calculation Methods”, Hideki YAMAMOTO, Johokiko. Inthis case, a combination of polymer 1, polymer 2 and the second solventis determined according to the following guideline. Specifically, Hansendissolution parameters for a certain polymer are plotted in athree-dimensional space, which is used as the center to form a sphereusing the interaction radius of the polymer. When the Hansen dissolutionparameter of the target solvent is plotted in the three-dimensionalspace, if the plot is inside the sphere, the target solvent is judged tobe a good solvent for the polymer whereas if the plot is outside thesphere, the target solvent is judged to be a poor solvent for thepolymer. According to this guideline, the first and second solvents areselected such that the first solvent is a good solvent for polymers 1and 2 while the second solvent is a good solvent for polymer 1 but apoor solvent for polymer 2.

More specifically, examples include the following combinations.

(i) Polymer 1: polystyrene, polymer 2: polymethyl methacrylate, andsecond solvent: cyclohexane;

(ii) Polymer 1: polystyrene, polymer 2: poly-D/L-lactic acid, and secondsolvent: cyclohexane;

(iii) Polymer 1: polymethyl methacrylate, polymer 2: polystyrene, andsecond solvent: ethyl acetate;

(iv) Polymer 1: polyethylene glycol, polymer 2: polystyrene, and secondsolvent: water;

(v) Polymer 1: polyvinylpyrrolidone, polymer 2: polystyrene, and secondsolvent: water; or

(vi) Polymer 1: poly-D/L-lactic acid, polymer 2: polystyrene, and secondsolvent: ethyl acetate.

Since the second solvent is a good solvent for polymer 1 but a poorsolvent for polymer 2, when an ultra-thin polymer film phase-separatedinto a sea-island structure is immersed in the second solvent, onlypolymer 1 as the island parts is dissolved in the second solvent, bywhich the island parts are selectively removed. Accordingly, the removedregions become the pores. As a result, a porous ultra-thin polymer filmcan be obtained.

According to this method, the pore diameter and the pore density can becontrolled by adjusting the mixed ratio (w/w) of the two types ofpolymers upon preparing the solution by dissolving the two types ofpolymers, by adjusting the rotation speed when the spin-coatingtechnique is used as a method for applying the solution onto thesubstrate, by adjusting the boiling point of the first solvent, or thelike.

More specifically, the pore diameter may be made larger while making thepore density lower by making the proportion (w/w) of polymer 1 in thesolution for dissolving the two types of polymers (polymers 1 and 2)higher. On the other hand, the pore diameter may be made smaller whilemaking the pore density higher by making the proportion (w/w) of polymer1 in the solution for dissolving the two types of polymers (polymers 1and 2) lower.

When a spin-coating technique is employed, the rotation speed can bemade higher to give a smaller pore diameter and a higher pore density.On the other hand, the rotation speed can be made lower to give a largerpore diameter and a lower pore density.

By making the boiling point of the first solvent higher, the heatingtemperature upon spin coating can be increased to give a larger porediameter and lower a pore density. On the other hand, the boiling pointof the first solvent can be lowered to give a smaller pore diameter anda higher pore density.

By using one or a combination of two or more of the above-describedmethods for controlling the pore diameter and the pore density, the porediameter and the pore density of the porous ultra-thin polymer film canarbitrarily be controlled.

In addition, the pore diameter distribution can be controlled asfollows. For example, when the spin-coating technique is employed, therotation rate upon spin coating can be decreased to increase the porediameter distribution. On the other hand, the rotation rate upon spincoating can be increased to make the pore diameter distribution smaller.

(2) Method that Uses Two Types of Solvents

According to this method, first, a polymer as a raw material isdissolved in a mixed solvent containing a good solvent for that polymerand a poor solvent having a higher boiling point than that of the goodsolvent in an arbitrary proportion to obtain a solution.

Examples of combinations of a polymer, a good solvent and a poor solventinclude those that are based on the calculation of the dissolutionparameters according to a method described, for example, in thedocument, “SP Values, Basis, Applications and Calculation Methods”,Hideki YAMAMOTO, Johokiko. In this case, a combination of a polymer, agood solvent and a poor solvent is determined according to the followingguideline. Specifically, Hansen dissolution parameters for a certainpolymer are plotted in a three-dimensional space, which is used as thecenter to form a sphere using the interaction radius of the polymer.When the Hansen dissolution parameter of the target solvent is plottedin the three-dimensional space, when the plot is inside the sphere, thetarget solvent is judged to be a good solvent for the polymer whereas ifthe plot is outside the sphere, the target solvent is judged to be apoor solvent for the polymer. According to this guideline, a group ofgood solvents and a group of poor solvents for a certain polymer aremade so as to select a combination of a good solvent and a poor solventwith a boiling point higher than that of said good solvent.

More specifically, examples include the following combinations.

(i) Polymer: poly-D,L-lactic acid, good solvent: ethyl acetate, and poorsolvent: dimethyl sulfoxide;

(ii) Polymer: polyglycolic acid, good solvent:1,1,1,3,3,3-hexafluoro-2-propanol, and poor solvent: ethyl acetate;

(iii) Polymer: polycaprolactone, good solvent: tetrahydrofuran (THF),and poor solvent: isopropyl alcohol;

(iv) Polymer: polydioxane, good solvent: dichloromethane, and poorsolvent: ethylene glycol;

(v) polymer: polymethyl methacrylate, good solvent: acetone, and poorsolvent: water;

(vi) polymer: cellulose acetate, good solvent: THF, and poor solvent:water;

(vii) polymer: cellulose acetate, good solvent: THF, and poor solvent:toluene; or

(viii) polymer: polystyrene, good solvent: THF, and poor solvent:dimethyl sulfoxide (DMSO).

The term “arbitrary proportion” means that the ratio (v/v) of goodsolvent:poor solvent is arbitrary, where the ratio (v/v) of goodsolvent:poor solvent is, for example, 100:1-100:10. The ratio (v/v) ofgood solvent:poor solvent is preferably 100:1-100:7, and more preferably100:1-100:5.

The concentration of the polymer in the solution is generally 1mg/ml-1000 mg/ml, preferably 3 mg/ml-100 mg/ml, and more preferably 5mg/ml-50 mg/ml.

Next, the resulting solution is applied onto a substrate, and the mixedsolvent is removed from the solution applied onto that substrate,thereby obtaining a porous ultra-thin polymer film.

The method for applying the solution onto the substrate is the same asdescribed above.

The method for removing the mixed solvent from the solution applied ontothe substrate is also the same as the above-described method forremoving the first solvent. When the good solvent with a lower boilingpoint is removed from the solution applied onto the substrate, anultra-thin polymer film dispersed with the poor solvent with a higherboiling point can be obtained transiently. Here, the poor solvent isfurther removed from the ultra-thin polymer film to obtain a porousultra-thin polymer film.

According to this method, the pore diameter and the pore density can becontrolled by adjusting the content of the poor solvent in the mixedsolvent containing the good solvent and the poor solvent, by adjustingthe rotation speed when the spin-coating technique is used as a methodfor applying the solution with the dissolved polymer onto the substrate,by adjusting the difference in the boiling point between the goodsolvent and the poor solvent, the solubility of the polymer in the poorsolvent and the temperature upon preparation, or the like.

More specifically, the content of the poor solvent in the mixed solventcontaining the good solvent and the poor solvent can be increased toincrease the pore diameter and the pore density. On the other hand, thecontent of the poor solvent in the mixed solvent containing the goodsolvent and the poor solvent can be decreased to decrease the porediameter and the pore density.

When a spin-coating technique is employed, the rotation speed can bemade higher to give a smaller pore diameter and a higher pore density.On the other hand, the rotation speed can be made lower to give a largerpore diameter and a lower pore density.

By making the difference in the boiling point between the good solventand the poor solvent greater, the pore diameter can be made larger whilethe pore density can be made lower. On the other hand, by making thedifference in the boiling point between the good solvent and the poorsolvent smaller, the pore diameter can be made smaller while the poredensity can be made higher.

By increasing the solubility of the polymer in the poor solvent, thepore diameter can be made smaller while the pore density can be madehigher. On the other hand, by decreasing the solubility of the polymerin the poor solvent, the pore diameter can be made larger while the poredensity can be made lower.

By using one or a combination of two or more of the above-describedmethods for controlling the pore diameter and the pore density, the porediameter and the pore density of the porous ultra-thin polymer film canarbitrarily be controlled.

In addition, the pore diameter distribution can be controlled asfollows. For example, when the spin-coating technique is employed, therotation rate upon spin coating can be decreased to increase the porediameter distribution. On the other hand, the rotation rate upon spincoating can be increased to make the pore diameter distribution smaller.

(3) Method for Using Microparticles as Molds for Textured Polymer Film

According to this method, first, a polymer is dissolved in a solvent toobtain a solution.

The polymer composes a porous ultra-thin polymer film of the presentinvention, whose specific examples have been described above.

The solvent may be any solvent as long as it is capable of dissolvingthe polymer, examples being ethyl acetate, dichloromethane, diethylether, methyl acetate, acetone, chloroform, methanol, tetrahydrofuran,dioxane, methyl ethyl ketone, benzene, acetonitrile, isopropyl alcohol,dimethoxyethane, ethylene glycol monoethyl ether (also known ascellosolve), ethylene glycol monoethyl ether acetate (also known ascellosolve acetate), ethylene glycol mono-normal-butyl ether (also knownas butyl cellosolve), ethylene glycol monomethyl ether (also known asmethyl cellosolve) toluene, N,N-dimethyl formamide anddimethylacetamide, preferably ethyl acetate, dichloromethane, diethylether, acetone, chloroform, tetrahydrofuran, dioxane, methyl ethylketone, acetonitrile, isopropyl alcohol, dimethoxyethane, N,N-dimethylformamide and dimethylacetamide, and more preferably ethyl acetate,dichloromethane, acetone, tetrahydrofuran, methyl ethyl ketone,acetonitrile, isopropyl alcohol and N,N-dimethyl formamide.

The concentration of the polymer in the solution is generally 1mg/ml-1000 mg/ml, preferably 3 mg/ml-100 mg/ml, and more preferably 5mg/ml-50 mg/ml.

Then, the resulting solution is applied onto a textured substrate andthe solvent is removed from the solution applied onto the substrate,thereby obtaining a porous ultra-thin polymer film.

The textured substrate may be, for example, a substrate having a polymerthin film having dispersed and fixed microparticles, a substrate havinga concave-convex pattern made by other method, or the like.

The method for applying the solution onto the substrate is the same asdescribed above.

The method for removing the solvent from the solution applied onto thesubstrate is also the same as the above-described method for removingthe first solvent.

Removal of the solvent from the solution applied onto the substrategives a porous ultra-thin polymer film that has the concave-convexpattern of the substrate replicated thereon.

Here, “a substrate having a polymer thin film having dispersed and fixedmicroparticles” exemplified as the textured substrate may be prepared,for example, as follows. First, a polymer is dissolved in a solvent toobtain a solution. The resulting solution is used to dilute and agitatethe dispersion of the microparticles. After applying the resultingdiluted solution onto the substrate, the solvent is removed from thediluted solution applied onto said substrate. Thus, a substrate having apolymer thin film having dispersed and fixed microparticles can beprepared.

The microparticles generally have a diameter of 20 nm-3000 nm(preferably a diameter of 100 nm-2000 nm, and more preferably a diameterof 500 nm-1500 nm), and formed from, for example, polystyrene particles,silica particles, dextran particles, polylactic acid particles,polyurethane microparticles, polyacrylic particles, polyethyleneimineparticles, albumin particles, agarose particles, iron oxide particles,titanium oxide microparticles, alumina microparticles, talcmicroparticles, kaolin microparticles, montmorillonite microparticles,hydroxyapatite microparticles or the like (preferably, polystyreneparticles, silica particles, dextran particles, titanium oxidemicroparticles, talc microparticles, montmorillonite microparticles orthe like). A dispersion can be obtained by dispersing thesemicroparticles in a solvent for dissolving a polymer that forms thefollowing polymer thin film.

A polymer that is used for forming a polymer thin film having dispersedand fixed microparticles may be, for example, polyvinyl alcohol,polyacrylic acid, polymethacrylic acid, sodium alginate, polyethyleneoxide, polyacrylic amide, polyvinylpyrrolidone, starch, collagen,pullulan, agar or the like, preferably polyvinyl alcohol, polyacrylicacid, sodium alginate, polyethylene oxide, polyacrylic amide,polyvinylpyrrolidone, starch or the like, and more preferably polyvinylalcohol, polyacrylic acid, starch or the like.

A solvent for dissolving the above-described polymer may be, forexample, water, acidic water, alkaline water, methanol, ethanol or thelike, and preferably water, alkaline water or the like.

The density of the microparticles in the dispersion is generally 0.1 wt%-20 wt %, preferably 0.5 wt %-10 wt %, and more preferably 1 wt %-5 wt%.

A method for applying the dispersion onto a substrate is notparticularly limited, and it may be applied onto a substrate, forexample, by a common technique such as a spin-coating technique, a spraycoating technique, a bar-coating technique, a dip coating technique orthe like. Alternatively, a solution may thinly applied onto a substrateby a common printing technique such as gravure printing, screenprinting, ink-jet printing or the like.

Thereafter, the solvent is removed from the diluted solution appliedonto the substrate. The method for removing the solvent is not limitedbut if the solution has been applied onto the substrate, for example, bya spin-coating technique, rotation can be continued to evaporate andremove the solvent. Alternatively, the solvent may be evaporated andremoved by heating. Alternatively, the solvent may be removed bydecompression. Alternatively, the solvent may be removed by combiningtwo or more of these methods for removing the solvent.

The film thickness of the polymer thin film having dispersed and fixedmicroparticles is generally 50 nm-1500 nm, preferably 100 nm-1000 nm,and more preferably 200 nm-800 nm.

The phrase “a substrate provided with concaves and convexes by othermethod” may be prepared, for example, by patterning the polymer thinfilm used upon dispersing and fixing the above-described microparticlesby a method such as lithography, printing, spraying or the like.

When the textured substrate is a substrate having a polymer thin filmhaving dispersed and fixed microparticles, the solvent is removed fromthe polymer solution applied onto the substrate to form an ultra-thinpolymer film. Then, the polymer thin film having dispersed and fixedmicroparticles may be dissolved in a solvent to peel off the porousultra-thin polymer film from the textured substrate to obtain afree-standing porous ultra-thin polymer film. Even when a substrateprovided with concaves and convexes by other method is used, afree-standing porous ultra-thin polymer film can be obtained by formingan ultra-thin polymer film and then dissolving the substrate itself.

A solvent for dissolving a polymer thin film or a substrate may be anysolvent as long as it dissolves a polymer thin film but not a porousultra-thin polymer film, which may, for example, be water, acidic water,alkaline water, methanol, ethanol or the like, or preferably water,alkaline water or the like.

The pore diameter, the pore density and the pore diameter distributionmay arbitrarily be controlled by adjusting the size, the density and thesize distribution of the microparticles used.

(4) Method for Using Precipitated Microparticles as Molds

According to this method, first, a polymer is dissolved in a solvent toobtain a solution.

The polymer is a polymer that composes a porous ultra-thin polymer filmof the present invention, whose specific examples are as describedabove.

The solvent may be any solvent as long as it can dissolve the polymer,whose specific examples are as described above.

The concentration of the polymer in the solution is generally 1mg/ml-1000 mg/ml, preferably 3 mg/ml-100 mg/ml, and more preferably 5mg/ml-50 mg/ml.

Next, a dispersion is obtained by precipitating microparticles from asalt-dissolved solution upon concentration utilizing the difference insolubility, or alternatively by dispersing microparticles that areinsoluble in the solution in advance.

The microparticles generally have a diameter of 20 nm-3000 nm(preferably a diameter of 100 nm-2000 nm, and more preferably a diameterof 500 nm-1500 nm), and they are not limited as long as they are notdissolved in a solvent for preparing a porous ultra-thin polymer filmbut dissolved in a solvent that does not dissolve the porous ultra-thinpolymer film. The microparticles may be formed, for example, frominorganic salts (for example, lithium bromide, sodium chloride, sodiumiodide, ammonium chloride, sodium hydrogen sulfate, sodium dihydrogenphosphate, calcium chloride, sodium acetate, sodium carbonate, sodiumhydrogen carbonate, disodium hydrogen phosphate, calcium carbonate,calcium oxide, calcium hydroxide, potassium thiocyanate, hydroxyapatite,etc.), silica, talc, kaolin, montmorillonite, polymers (for example,polystyrene, dextran, polyphenol, polyamide, acrylics,polyethyleneimine, agarose, etc.), metal oxides (for example, alumina,iron oxide, titanium oxide, etc.) and metals (for example, silver,copper, iron, zinc, aluminum, etc.), and preferably formed from lithiumbromide, calcium carbonate, silica, talc, titanium oxide or the like.

Next, the above-described dispersion is applied onto a substrate andthen the solvent is removed from the dispersion applied onto thesubstrate to obtain an ultra-thin polymer film.

The method for applying the dispersion onto the substrate is notparticularly limited, but the dispersion may be applied onto thesubstrate, for example, by a common technique such as a spin-coatingtechnique, a spray coating technique, a bar-coating technique, a dipcoating technique or the like. Alternatively, the solution may thinlyapplied onto the substrate by a common printing technique such asgravure printing, screen printing, ink-jet printing or the like.

Thereafter, the solvent is removed from the dispersion applied onto thesubstrate. Although the method for removing the solvent is also notlimited, if the dispersion has been applied onto a substrate, forexample, by a spin-coating technique, rotation can be continued toevaporate and remove the solvent. Alternatively, the solvent may beevaporated and removed by heating. Alternatively, the solvent may beremoved by decompression. Alternatively, the solvent may be removed bycombining two or more of these methods for removing the solvent.

Next, the resulting ultra-thin polymer film is immersed in a solventthat can dissolve the above-described microparticles to remove saidmicroparticles, thereby obtaining a porous ultra-thin polymer film.

The term “a solvent that can dissolve microparticles” is a solvent thatdoes not dissolve an ultra-thin polymer film but that can dissolvemicroparticles. The solvent may appropriately be selected according tothe type of the polymer and the type of the microparticles. Specificexamples of the solvents include water, acidic water, alkaline water,alcohol, dimethyl formamide, cyclohexane, acetone, ethyl acetate or thelike. For example, sodium bromide can be dissolved in acetone,thiocyanated potassium can be dissolved in dimethyl formamide, metalsand calcium carbonate can be dissolved in acidic water, and silica canbe dissolved in alkaline water.

The solvent can dissolve and remove the microparticles. The parts wherethe microparticles have been removed become the pores. As a result, aporous ultra-thin polymer film can be acquired.

The pore diameter, the pore density and the pore diameter distributionmay arbitrarily be controlled by adjusting the size, the density and thesize distribution of the microparticles used.

(5) Method for Using Textured Substrate as Mold

According to this method, an ultra-thin polymer film built on asubstrate is heated at a glass-transition temperature or higher and thensaid ultra-thin polymer film is compressed with a separately preparedtextured substrate, thereby obtaining a porous ultra-thin polymer film.

The substrate, the polymer and the textured substrate are the same asdescribed above.

Compression of the ultra-thin polymer film heated at a glass-transitiontemperature or higher with the textured substrate gives a porousultra-thin polymer film which has replicated the concave-convex patternof the substrate.

(6) Method for Dispersing Microbubbles

According to this method, a polymer as a raw material is dissolved in asolvent to obtain a solution and microbubbles are dispersed in theresulting solution. The microbubble-dispersed solution is applied onto asubstrate and the solvent is removed from the solution applied onto thesubstrate, thereby obtaining a porous ultra-thin polymer film.

The polymer, the solvent, the substrate and the like are the same asdescribed above.

The method for dispersing microbubbles in the solution may be carriedout according to a known method.

After the removal of the solvent, the microbubble parts become thepores. As a result, a porous ultra-thin polymer film can be obtained.

(7) Peeling Porous Ultra-Thin Polymer Film from Substrate

In the case where a porous ultra-thin polymer film is obtained in a formof a complex with a substrate according to any of the above-describedmethods, the porous ultra-thin polymer film can be peeled off from thesubstrate to obtain a free-standing porous ultra-thin polymer film.

Examples of methods for peeling off the porous ultra-thin polymer filmfrom the substrate include a method in which a water-soluble sacrificialfilm is provided between the porous ultra-thin polymer film and thesubstrate, and a method in which a sacrificial film which dissolves in asolvent that does not dissolve the porous ultra-thin polymer film(hereinafter, also referred to as “other sacrificial film”) is providedbetween the porous ultra-thin polymer film and the substrate.

According to the method in which a water-soluble sacrificial film isprovided between the porous ultra-thin polymer film and the substrate,the water-soluble sacrificial film is provided in advance between theporous ultra-thin polymer film and the substrate and then it is removedwith water, thereby peeling off the porous ultra-thin polymer film fromthe substrate. Examples of the water-soluble sacrificial films includeat least one film selected from the group consisting of a polyvinylalcohol film, a polyacrylate film, a polymethacrylate film, a sodiumalginate film, a polyethylene oxide film, a polyacrylic amide film, apolyvinylpyrrolidone film, a starch film, a carboxymethyl cellulosefilm, a collagen film, a pullulan film, an agar film, a silicon film andthe like.

According to the method in which a sacrificial film which dissolves in asolvent that does not dissolve the porous ultra-thin polymer film isprovided between the porous ultra-thin polymer film and the substrate, apolystyrene film, a polyolefin film, a polymethyl methacrylate film, apolyphenol film or the like is provided in advance between the porousultra-thin polymer film and the substrate, which is then treated withcyclohexane, cyclohexane, acetone, methanol or the like, respectively,thereby peeling off the porous ultra-thin polymer film from thesubstrate.

The film thickness of the water-soluble sacrificial film or the othersacrificial film is generally 5 nm-1000 nm, preferably 5 nm-500 nm, morepreferably 10 nm-300 nm, still more preferably 10 nm-200 nm, andparticularly preferably 10 nm-100 nm. The water-soluble sacrificial filmor the other sacrificial film may be formed according to a known method.

The water-soluble sacrificial film can be removed with water from thecomplex of the substrate, the water-soluble sacrificial film and theporous ultra-thin polymer film so as to obtain a free-standing porousultra-thin polymer film. Briefly, the water-soluble sacrificial film canbe dissolved with water to give a free-standing porous ultra-thinpolymer film in water.

The thus-resulting free-standing porous ultra-thin polymer film may bepicked up and placed onto another substrate and water may be removedfrom this picked up porous ultra-thin polymer film to obtain a porousultra-thin polymer film in a dry state.

The term “another substrate” refers to the same substrate as describedabove.

Alternatively, the resulting free-standing porous ultra-thin polymerfilm may be picked up with a mesh to produce a complex of the porousultra-thin polymer film and the mesh.

The term “mesh” is as described above.

(8) Support Membrane

In the case where a porous ultra-thin polymer film of the presentinvention is obtained in a form of a complex with a substrate accordingto any of the above-described methods, this porous ultra-thin polymerfilm may further be provided with a water-soluble support membranethereon. By doing so, a complex of the substrate, the porous ultra-thinpolymer film and the water-soluble support membrane can be obtained,where the substrate has the porous ultra-thin polymer film thereon andthe porous polymer thin film, in turn, has the water-soluble supportmembrane thereon.

Examples of the water-soluble support membrane include at least one filmselected from the group consisting of a polyvinyl alcohol film, apolyacrylate film, a polymethacrylate film, a sodium alginate film, apolyethylene oxide film, a polyacrylic amide film, apolyvinylpyrrolidone film, a starch film, a carboxymethyl cellulosefilm, a collagen film, a pullulan film, an agar film, a silicon film andthe like.

The film thickness of the water-soluble support membrane is generally 50nm-20000 nm, preferably 100 nm-10000 nm, more preferably 200 nm-5000 nm,still more preferably 500 nm-5000 nm, and particularly preferably 700nm-5000 nm. The water-soluble support membrane may be formed accordingto a known method.

7. Ultra-Thin Polymer Film Phase-Separated into Sea-Island Structure

The present invention provides an ultra-thin polymer film that has beenphase-separated into a sea-island structure (hereinafter, referred to asan “ultra-thin polymer film of the present invention”), which can beobtained, on a substrate, by: dissolving two types ofmutually-immiscible polymers, namely, a first polymer and a secondpolymer, in a solvent in an arbitrary proportion to obtain a solution;applying the resulting solution onto the substrate; and removing thesolvent from the solution applied onto the substrate.

Hereinafter, the solvent for dissolving the first and the secondpolymers may be referred to as a “first solvent”.

The phrase “two types of mutually-immiscible polymers, namely, a firstpolymer and a second polymer” refers to two types of polymers which donot mix with each other in solid states. Hereinafter, among the twotypes of polymers, the polymer that forms the island parts upon phaseseparation into the sea-island structure is referred to as the firstpolymer while the polymer other than the island parts is referred to asthe second polymer. Examples of such a combination of the first polymerand the second polymer will be recited below.

The film thickness of the ultra-thin polymer film of the presentinvention, similar to the porous ultra-thin polymer film of the presentinvention, is generally 10 nm-1000 nm. While the film thickness of theultra-thin polymer film of the present invention may appropriately bedetermined according to the use thereof, it is preferably 20 nm-800 nm,more preferably 30 nm-600 nm, still more preferably 40 nm-400 nm, andparticularly preferably 50 nm-200 nm.

The ultra-thin polymer film of the present invention has a plurality ofisland parts of the sea-island structure on its surface. Herein, theterm “surface” refers to the top surface or the back surface of theultra-thin film. The island parts on the surface may be provided at anydensity as long as there are multiple island parts. While the densitymay appropriately be determined according to usage, the density of theisland parts on the surface (numbers/μm²) is generally0.005/μm²-100/μm², preferably 0.05/μm²-50/μm², more preferably0.1/μm²-30/μm², and still more preferably 0.5/μm²-20/μm².

In the ultra-thin polymer film of the present invention, the islandparts may be made into any shape which may, for example, besubstantially disk-like, oval, rectangular, square or the like when seenfrom the top, but in general they are substantially disk-like. Thesubstantially disk-like island parts may merge with each other.

While the size of the island parts of the sea-island structure in theultra-thin polymer film of the present invention is not particularlylimited and may appropriately be determined according to purpose, it hasgenerally the same size as the pore diameter of the porous ultra-thinpolymer film of the present invention. Accordingly, the size of theisland parts of the sea-island structure is preferably 0.01 μm-500 μm,more preferably 0.03 μm-100 μm, still more preferably 0.1 μm-5 μm, andparticularly preferably 0.5 μm-3 μm.

Alternatively, the size of the island parts of the sea-island structureis preferably in a range that is larger than 1 μm and smaller or equalto 25 μm, more preferably in a range that is larger than 1 μm andsmaller or equal to 20 μm, still more preferably in a range that islarger than 1 μm and smaller or equal to 18 μm, and particularlypreferably in a range that is larger than 1 μm and smaller or equal to15 μm.

A plurality of island parts with either the same or different sizes maybe provided in a single ultra-thin film.

When a plurality of island parts with different sizes are provided, thesize distribution of the island parts may, for example, be ±10% or more.In some embodiments of the present invention, the size distribution ofthe island parts is ±20% or more, preferably ±25% or more, morepreferably ±30% or more, and still more preferably ±35% or more (forexample, ±35% or more, ±40% or more, ±45% or more, or ±50% or more).

Furthermore, in some embodiments of the present invention, the sizedistribution ranges from the above-mentioned lower limit ±10% or moreto, for example, 1200% or less, ±150% or less, ±100% or less, ±50% orless, ±40% or less, ±30% or less, ±20% or less or ±15% or less.

In some other embodiments of the present invention, the sizedistribution ranges from the above-mentioned lower limit ±20% or more(for example, ±20% or more, ±25% or more, ±30% or more, ±35% or more,±40% or more, ±45% or more, or ±50% or more) to ±200% or less or ±150%or less.

Herein, the term “size distribution” refers to a value calculated asfollows. Briefly, a size distribution of the island parts is calculatedas σ/μ by approximating the distributions of the sizes to give thenormal distribution, where the mean is μ and the deviation is σ².

On the other hand, when a plurality of island parts with different sizesare provided, the size difference between the island part with themaximum size and the island part with the minimum size is generally 0.01μm-500 μm, preferably 0.03 μm-100 μm, still more preferably 0.1 μm-5 μm,and particularly preferably 0.5 μm-3 μm.

In a preferable embodiment of an ultra-thin film of the presentinvention, the ratio of a island part size to a film thickness of theultra-thin polymer film (island part size (μm)/film thickness (μm)) is,for example, 0.1-50, preferably 0.2-40, more preferably 0.3-20 andparticularly preferably 0.5-15.

Moreover, the island parts may be provided on both of the top and backsurfaces of the ultra-thin polymer film, similar to the pores shown inFIG. 8(a), or only on one of the surfaces (only on the top surface oronly on the back surface). When the island parts are provided on both ofthe top and back surfaces of the porous ultra-thin polymer film, thedensity of the island parts may be the same or different between the topand back surfaces. The arrangement of such island parts mayappropriately be determined according to usage.

An ultra-thin polymer film of the present invention may have any sizeand shape. The size is 0.05 mm-50 cm, preferably 0.1 mm-10 cm, and morepreferably 0.3 mm-5 cm. The shape is not particularly limited but it maybe, for example, a flat shape such as a circle, an oval, a square, ahexagon, a ribbon shape, a string shape, a multibranched shape or a starshape, or a three-dimensional shape such as a tube, a convex, a shape ofa face mask or a shape of a handprint. The shape of an ultra-thinpolymer film may appropriately be determined according to usage.

The ultra-thin polymer film of the present invention may also be used toprepare a porous ultra-thin polymer film. In this case, the ultra-thinpolymer film that has been phase-separated into a sea-island structureis immersed in a second solvent which is a good solvent for the firstpolymer as the island parts but a poor solvent for the second polymerother than the island parts to remove the island parts, therebyobtaining a porous ultra-thin polymer film.

A combination of the first and second polymers and the second solventmay be based on the calculation of the dissolution parameters accordingto a method described, for example, in the document, “SP Values, Basis,Applications and Calculation Methods”, Hideki YAMAMOTO, Johokiko. Inthis case, a combination of the first and second polymers and the thirdsolvent is determined according to the following guideline.Specifically, Hansen dissolution parameters for a certain polymer areplotted in a three-dimensional space, which is used as the center toform a sphere using the interaction radius of the polymer. When theHansen dissolution parameter of the target solvent is plotted in thethree-dimensional space, if the plot is inside the sphere, the targetsolvent is judged to be a good solvent for the polymer whereas if theplot is outside the sphere, the target solvent is judged to be a poorsolvent for the polymer. According to this guideline, the first andsecond solvents are selected such that the first solvent is a goodsolvent for the first and second polymers while the second solvent is agood solvent for the first polymer but a poor solvent for the secondpolymer.

More specifically, examples include the following combinations.

(i) First polymer: polystyrene, and second polymer: polymethylmethacrylate;

(ii) First polymer: polystyrene, and second polymer: poly-D/L-lacticacid;

(iii) First polymer: polymethyl methacrylate, and second polymer:polystyrene;

(iv) First polymer: polyethylene glycol, and second polymer:polystyrene;

(v) First polymer: polyvinylpyrrolidone, and second polymer:polystyrene; or

(vi) First polymer: poly-D/L-lactic acid, and second polymer:polystyrene.

In the case of Combination (i) above, the second solvent is, forexample, cyclohexane.

In the case of Combination (ii) above, the second solvent is, forexample, cyclohexane.

In the case of Combination (iii) above, the second solvent is, forexample, ethyl acetate.

In the case of Combination (iv) above, the second solvent is, forexample, water.

In the case of Combination (v) above, the second solvent is, forexample, water.

In the case of Combination (vi) above, the second solvent is, forexample, ethyl acetate.

Since the second solvent is a good solvent for the first polymer but apoor solvent for the second polymer, when an ultra-thin polymer filmthat has been phase-separated into a sea-island structure is immersed init, only the first polymer as the island parts is dissolved in thesecond solvent and thus the island parts are selectively removed.Accordingly, the removed regions become the pores. As a result, a porousultra-thin polymer film can be obtained.

The ultra-thin polymer film of the present invention may be produced asfollows.

First, two types of mutually-immiscible polymers are dissolved in asolvent in an arbitrary proportion to obtain a solution.

The term “arbitrary proportion” means that the ratio (w/w) of firstpolymer:second polymer is arbitrary, where the ratio (w/w) of firstpolymer:second polymer may, for example, be 1:9-5:5. The ratio (w/w) offirst polymer:second polymer is preferably 1:9-4:6, and more preferably1:9-3:7.

The first solvent is not limited as long as it is capable of dissolvingthe above-mentioned two types of polymers but generally it is at leastone type of solvent selected from the group consisting ofdichloromethane, diethyl ether, methyl acetate, acetone, chloroform,methanol, tetrahydrofuran, dioxane, ethyl acetate, methyl ethyl ketone,benzene, acetonitrile, isopropyl alcohol, dimethoxyethane, ethyleneglycol monoethyl ether (also known as cellosolve), ethylene glycolmonoethyl ether acetate (also known as cellosolve acetate), ethyleneglycol mono-normal-butyl ether (also known as butyl cellosolve),ethylene glycol monomethyl ether (also known as methyl cellosolve)toluene, N,N-dimethyl formamide and dimethylacetamide. The solvent ispreferably at least one type of solvent selected from the groupconsisting of dichloromethane, diethyl ether, acetone, chloroform,tetrahydrofuran, dioxane, ethyl acetate, methyl ethyl ketone,acetonitrile, isopropyl alcohol, dimethoxyethane, N,N-dimethyl formamideand dimethylacetamide, more preferably at least one type of solventselected from the group consisting of dichloromethane, acetone,tetrahydrofuran, ethyl acetate, methyl ethyl ketone, acetonitrile,isopropyl alcohol and N,N-dimethyl formamide, and more preferably atleast one type of solvent selected from the group consisting ofdichloromethane, tetrahydrofuran and ethyl acetate.

The total weight concentration of the polymer in the solution isgenerally 0.1 wt %-20 wt %, preferably 0.3 wt %-10 wt %, and morepreferably 0.5 wt %-2 wt %.

Next, the resulting solution is applied onto a substrate, after whichthe solvent is removed from the solution applied onto the substrate,thereby obtaining an ultra-thin polymer film that has beenphase-separated into a sea-island structure.

A method for applying the solution onto the substrate is notparticularly limited and the solution may be applied onto the substrate,for example, by a common technique such as a spin-coating technique, aspray coating technique, a bar-coating technique, a dip coatingtechnique or the like. Alternatively, a solution may be thinly appliedonto the substrate by a common printing technique such as gravureprinting, screen printing, ink-jet printing or the like.

Subsequently, the solvent is removed from the solution applied onto thesubstrate. A method for removing the solvent is also not particularlylimited. For example, if the solution has been applied onto thesubstrate by a spin-coating technique, rotation can be continued toevaporate and remove the solvent. Alternatively, the solvent may beevaporated and removed by heating. Alternatively, the solvent may beremoved by decompression. Alternatively, the solvent may be removed bycombining two or more of these methods for removing the solvent.

According to this method, the size and the density of the island partscan be controlled by adjusting the mixed ratio (w/w) of the two types ofpolymers upon preparing the solution for dissolving the two types ofpolymers, by adjusting the rotation speed if the spin-coating techniqueis used as a method for applying the solution onto the substrate, byadjusting the boiling point of the solvent, or the like.

More specifically, the proportion (w/w) of the first polymer in thesolution containing the two types of polymers (first and secondpolymers) can be made higher to increase the size of the island partswhile decreasing the density of the island parts. On the other hand, theproportion (w/w) of the first polymer in the solution containing the twotypes of polymers (first and second polymers) can be made lower todecrease the size of the island parts while increasing the density ofthe island parts.

If a spin-coating technique is employed, the rotation speed can be madehigher to give a smaller size and a higher density of the island parts.On the other hand, the rotation speed can be made lower to give a largersize and a lower density of the island parts.

By making the boiling point of the first solvent higher, the heatingtemperature upon spin coating can be increased to give a larger size anda lower density of the island parts. On the other hand, the boilingpoint of the solvent can be lowered to give a smaller size and a higherdensity of the island parts.

By employing one or a combination of two or more of the above-describedmethods for controlling the size and the density of the island parts,the size and the density of the island parts of the ultra-thin polymerfilm can arbitrarily be controlled.

In addition, the size distribution of the island parts can be controlledas follows. For example, if the spin-coating technique is employed, therotation rate upon spin coating can be decreased to increase the sizedistribution of the island parts. On the other hand, the rotation rateupon spin coating can be increased to make the size distribution of theisland parts smaller.

8. Nanodisc Mer Film Having Island Parts Obtained by Dissolving SeaParts of Sea-Island Structure

By reversing the ratio of first polymer:second polymer described in theabove section “7. Ultra-thin polymer film phase-separated intosea-island structure”, the composition of the sea-island polymer can bereversed.

For example, according to the above-described example, in the case of(vi), i.e., first polymer: poly-D/L-lactic acid and second polymer:polystyrene, cyclohexane can be used as the second solvent to obtain thedisk-like ultra-thin polymer film of the example shown in FIG. 12.

In a case where a second solvent which is a poor solvent for the firstpolymer but a good solvent for the second polymer is selected forimmersing the ultra-thin polymer film that has been phase-separated intoa sea-island structure, only the second polymer as the sea parts isdissolved in the second solvent, by which the sea parts are selectivelyremoved. As a result, an ultra-thin polymer film composed of the islandparts, namely, a nanodisc, can be obtained.

The resulting nanodisc will have the dimensions of the island partsdescribed in the above section “7. Ultra-thin polymer filmphase-separated into sea-island structure”.

EXAMPLES

Hereinafter, the present invention will be described more specificallyby way of examples, although the present invention should not be limitedto these examples.

Example 1-1: Method Using Two Types of Polymers

Polystyrene (PS) and polymethyl methacrylate (PMMA) were purchased from

Chemco Scientific Co., Ltd. and Sigma-Aldrich, respectively. Theircharacteristics are shown in Table 1. As polyvinyl alcohol (PVA, 10mg/mL), one with a molecular weight Mw of ca. 22 kDa was purchased fromKanto Chemicals Co. These polymers were used without purification.

TABLE 1 Characteristics and physical properties of PS and PMMA (in bulkstates) Polymers Mw (kDa) Mw/Mn Density at 25° C. (g/cm³) Tg (° C.) PS170 1.06 1.05 100 PMMA 120 1.8-2.0 1.19 105

A silicon (100) wafer, namely, an oxide coating layer, with a thicknessof 200 nm was purchased from KST World Co., cut into 20×20 mm² and usedas a substrate. The substrate was immersed in sulfuric acid and 30%hydrogen peroxide (3:1, v/v) at 120° C. for 10 minutes, washed withion-exchange water (18 MΩ cm), and dried in a nitrogen stream. Thecontact angle of water was confirmed to be 44.5° with a contact anglemeasurement device (DM-301, Kyowa Interface Science Co., Ltd.).

PS and PMMA were dissolved in dichloromethane at different weight ratios(PS: PMMA=0:10, 1:9, 2:8 and 3:7 w/w) to give mixed solutions. The totalweight concentrations of the polymers in the solutions were 10 mg/mL,and polymer blend nanosheets were prepared with spin coater MS-A100(MIKASA Co., Ltd.).

First, an aqueous PVA solution (1.0 wt %) was spin-coated on the siliconsubstrate at a rotation speed of 3000 rpm to produce a sacrificial film,on which a polymer blend solution was spin-coated at the rotation speedof 1000, 3000, 5000 or 7000 rpm for 60 seconds. The resultant wasimmersed in ion-exchange water together with the substrate to dissolvethe PVA sacrificial film, by which the free-standing polymer blendnanosheet began to peel off. The sheet was manipulated with tweezers tobe picked up and placed onto a silicon substrate with either top or backsurface facing up. Cyclohexane is a good solvent for PS but a poorsolvent for PMMA. When the polymer blend nanosheet on the siliconsubstrate was immersed together with the substrate in cyclohexane, onlythe PS regions were selectively removed. This was carried out for bothtop and rear surfaces and the surface structures were observed. All ofthe manipulations were conducted in a clean room (class 10,000conditions) at room temperature (25° C.) and humidity (35% RH).

In order to observe the surface structures, an intermolecular forcemicroscope (KEYENCE VN-8000 NANOSCALE hybrid microscope) and a fieldemission-type electron microscope (FE-SEM, Hitachi S-5500) were used.The former was used with a silicon-made cantilever (KEYENCE, OP-75041)in a tapping mode (1.67-3.33 Hz) to scan the surfaces of the nanosheets.The AFM images were processed with VN Analyzer (KEYENCE) and ImageJ(NIH) software. The latter was used for observing the cross-sections ofthe nanosheets. The nanosheets were immersed in liquid nitrogen for 10minutes for freeze-fracture. The cross-section was spattered withgold-palladium (Au—Pd) and observed at an accelerating voltage of 5 kV.The image was processed with ImageJ software.

Typical AFM images are shown in FIG. 1 where the PS:PMMA ratios of thepolymer blend solutions were 0:10, 1:9, 2:8 and 3:7 w/w, and therotation rate was 5000 rpm. The images (a1)-(d1) in the top row in FIG.1 are the AFM images of the polymer blend nanosheets made of PS andPMMA. The bright regions are the phase-separated PS regions. The images(a2)-(d2) in the middle row in FIG. 1 are the AFM images of the topsurfaces of the nanosheets whose PS regions have been dissolved withcyclohexane to leave the PMMA regions. The bright regions in the top rowcan be appreciated to have become dark. These are the pores resultingfrom the removal of the PS regions. The images (a3)-(d3) in the bottomrow in FIG. 1 are the AFM images of the rear surfaces of the nanosheetswhose PS regions have been dissolved with cyclohexane to leave the PMMAregions. Since both top and rear surfaces have similar structure, thepores are suggested to be passing through.

The AFM images in FIG. 1 show the nanosheets with the PS:PMMA ratios of(a) 0:10, (b) 1:9, (c) 2:8 and (d) 3:7 (w/w), respectively, from theleft. In the case of the PMMA homopolymer nanosheet, the top surface wasflat and no phase separation structure could be found. In addition, noporous structure was found with cyclohexane treatment. On the otherhand, phase separation structures were observed in the PS/PMMA blendnanosheet while the total area of the phase-separated PS regionsincreased with the increase in the proportion of PS. The pores wereminute and numerous at the PS:PMMA ratio of 1:9 whereas the pores mergedwith each other and became larger and less in number at the PS:PMMAratio of 2:8. At the PS:PMMA ratio of 3:7, the pores completely mergedwith each other and formed intricate grooves.

FIG. 2 shows AFM images of the nanosheets prepared from a polymer blendsolution prepared at a PS:PMMA ratio of 2:8 (w/w) and the rotationspeeds of 1000, 3000, 5000 and 7000 rpm, respectively, where definitionsfor the top, middle and bottom rows are the same as those shown inFIG. 1. Although the total area of the phase-separated PS remainsunchanged, the number of pores tended to increase while the size of thepores tended to decrease with the increase in the rotation speed, withrespect to the density and the size of the pores obtained at therotation speed of 1000 rpm. This was considered to be due to fasterdrying and fixing before the phase-separated PS regions merge and becomelarger since higher rotation speed results in faster drying of thenanosheets. At varied rotation speeds, the average sizes of the pores inthe top and the back surfaces were 187.2±33.9/194.1±72.9 (topsurface/back surface) at 1000 rpm, and 105.4±25.1/108.2±20.9 nm (topsurface/back surface) at 7000 rpm.

Table 2 summarizes the film thicknesses, the pore diameters and the poredensities of the nanosheets prepared at the PS:PMMA ratios of 1:9 and2:8 and the rotation speeds of 1000, 3000, 5000 and 7000 rpm. The filmthickness tended to decrease with the rotation speed. The mixture ratioof 2:8 showed a tendency to give thicker sheets. The pore diameters werelarger at 2:8 than 1:9, which tended to decrease with the rotationspeed. The pore density was smaller at 2:8 than 1:9, which tended toincrease with rotation speed.

Furthermore, the pore diameter distribution tended to increase with thedecrease in the rotation rate upon spin coating.

TABLE 2 Polymer mixture ratio PS:PMMA = 1:9 w/w PS:PMMA = 2:8 w/wRotation speed 1000 rpm 3000 rpm 5000 rpm 7000 rpm 1000 rpm 3000 rpm5000 rpm 7000 rpm Film thickness 97.6 ± 1.3 56.7 ± 1.9  42.6 ± 0.7  38.1± 1.1 110.2 ± 2.0  60.6 ± 2.9 44.4 ± 1.0 40.4 ± 1.3 (nm) Pore diameter102.2 ± 25.4 77.2 ± 15.5 70.2 ± 11.2 66.0 ± 9.5 190.7 ± 53.4 136.4 ±34.5 115.3 ± 30.0 106.8 ± 23.2 (nm) Pore diameter 24.9% 20.1% 16.0%14.4% 28.0% 25.3% 26.0% 21.7% distribution value Pore density 11.6 23.427.5 28.0 4.8 7.3 8.8 8.2 (/μm²)

A scanning electron microscope (SEM) was used to collect the informationof the cross-sections and the pores in the depth direction for the ofporous nanosheets obtained by treating PS/PMMA blend nanosheets withcyclohexane (FIG. 3). As can be appreciated from the cross-sectionalimages, the PS regions have flat oval structures distributed in thenanosheets. When the PS regions exposed at the surface of the nanosheetare removed with cyclohexane, they results in pores. When a PS regionexposed at both top and rear surfaces is removed with cyclohexane, itforms a penetrating pore. Moreover, when a PS region retained within thefilm is removed with cyclohexane, a cavity is found to be formed insidethe film. When the surfaces of the nanosheets are obliquely seen with aSEM one by one, pores having different sizes at the top and backsurfaces exist. This is considered to result from reflecting thedifference in the exposure of the phase-separated flat oval PS regionsbetween the top and the rear surfaces of the nanosheet.

Hence, two types of polymers that are mutually immiscible in solidstates are dissolved in a common solvent, which is casted to obtain ablend nanosheet that has been phase-separated into a sea-islandstructure and treating with a good solvent for the polymer making up theisland parts to produce a porous nanosheet.

Example 1-2: Method Using Two Types of Polymers

PS (Mw: 1701(D) and poly-D,L-lactic acid (Mw: 300 kD) were dissolved inethyl acetate at different weight ratios (PS: poly-D,L-lactic acid=3:7w/w) to give a mixed solution. The total weight concentration of thepolymer in the solution was 10 mg/mL and a polymer blend nanosheet wasprepared with spin coater MS-A100 (MIKASA Co., Ltd.).

First, an aqueous PVA solution (10 mg/mL) was spin-coated on a siliconsubstrate at a rotation speed of 3000 rpm to generate a sacrificialfilm, on which a polymer blend solution was spin-coated at a rotationspeed of 1000, 3000, 5000 or 7000 rpm for 60 seconds. When the resultantwas immersed in ion-exchange water together with the substrate, the PVAsacrificial film was dissolved, by which the free-standing polymer blendnanosheet began to peel off. The sheet was manipulated with tweezers tobe picked up and placed onto a silicon substrate with the top surfacefacing up.

Cyclohexane is a good solvent for PS but a poor solvent forpoly-D,L-lactic acid. When the polymer blend nanosheet on the siliconsubstrate is immersed together with the substrate in cyclohexane, onlythe PS regions were selectively removed. All of these manipulations werecarried out in a clean room (class 10,000 conditions) at roomtemperature (25° C.) and humidity (35% RH).

The results are shown in FIG. 4 and Table 3. The top row in FIG. 4 showthe phase separation states of the nanosheets prior to the cyclohexanetreatment, the bottom row show the nanosheets with pores made bycyclohexane treatment. The nanosheets prepared at the rotation speeds of1000, 3000, 5000 and 7000 rpm, respectively are shown from the left.With reference to Table 2, the film thickness can be found to becomethinner with the increase in the rotation speed. In addition, the porediameter tends to become smaller while the pore density tends to becomehigher with the increase in the rotation speed.

Furthermore, the pore diameter distribution was found to have a tendencyto increase with the decrease in the rotation rate upon spin coating.

TABLE 3 Polymer mixture ratio PS:D,L-PLA = 3:7 w/w Rotation speed 1000rpm 3000 rpm 5000 rpm 7000 rpm Film thickness (nm) 76.8 ± 2.3  40.8 ±2.6  32.6 ± 1.3  26.2 ± 0.8  Pore diameter (μm) 0.49 ± 0.24 0.33 ± 0.150.24 ± 0.10 0.23 ± 0.11 Pore diameter distribution value 49.0% 45.5%41.7% 47.8% Pore density (/μm2) 1.2  2.4  2.7  2.9 

Example 2: Method Using Two Types of Solvents

All of the manipulations were carried out by providing a spin coater(Opticoat MS-A 100, MIKASA) in a clean room (class 10,000). A siliconsubstrate (KST World) was cut into 2.0 cm×2.0 cm, immersed in sulfuricacid/30% hydrogen peroxide water (3/1, v/v) at 120° C. for 10 minutesand then washed with deionized water (resistivity 18 MS/cm). Mixedsolvents of ethyl acetate and dimethyl sulfoxide (DMSO) (ethylacetate:DMSO=100:1, 100:3 and 100:5, v/v) was used to adjustpoly-D,L-lactic acid (Mw: 300 kDa) to have final concentrations of 30mg/mL. The substrate was placed in the spin coater, each of the preparedsolutions were dropped and subjected to spin coating at the rotationspeed of 1000, 3000, 5000 or 7000 rpm for 60 seconds (room temperature32° C., humidity 32%). The prepared nanosheets visually had white spots.

An aqueous polyvinyl alcohol solution (Mw: 22,000, Kanto Chemical, 100mg/mL) was dropped on the formed poly-D,L-lactic acid nanosheet on thesilicon substrate. A PVA film as a support membrane was formed on thepoly-D,L-lactic acid nanosheet, and dried using a hot plate (HOT PLATENHP-M20, NISSIN) (30° C., 15 minutes). Subsequently, the poly-D,L-lacticacid nanosheet together with the PVA film was peeled off from thesilicon substrate, and subjected to vacuum drying using a vacuum dryer(KVO-300, AS ONE) (overnight). The structure of the top surface wasscanned using an intermolecular force microscope (KEYENCE VN-8000NANOSCALE hybrid microscope) with a silicon-made cantilever (KEYENCE,OP-75041) in a tapping mode (1.67-3.33 Hz). The AFM images wereprocessed with a VN Analyzer (KEYENCE) and ImageJ (NIH) software. InFIG. 5, the images in the top row (a1)-(c1) and the second row (a2)-(c2)show top and back surfaces of ethyl acetate:DMSO at 100:1, the images inthe third row (d1)-(f1) and the fourth row (d2)-(f2) show top and backsurfaces of ethyl acetate:DMSO at 100:3, the images in the fifth row(g1)-(i1) and the sixth row (g2)-(i2) show top and back surfaces ofethyl acetate:DMSO at 100:5. In FIG. 5, the rotation speeds are 1000,3000 and 5000 rpm, respectively, from the left. Additionally, Table 4summarizes characteristics of nanosheets obtained when the rotationspeeds were altered for the three types of systems with different mixedsolvent ratios.

TABLE 4 Solvent mixture ratio ethyl acetate:DMSO = 100:3 v/v 100:1 v/v100:3 v/v 100:5 v/v Rotation speed 1000 rpm 3000 rpm 5000 rpm 3000 rpmFilm thickness (nm) 583.8 ± 48.8  296.8 ± 18.0  241.0 ± 18.4 275.1 ±17.7  296.8 ± 18.0  413.8 ± 31.3 Pore diameter (μm) 2.1 ± 1.0 1.8 ± 1.1 1.6 ± 0.6 0.6 ± 0.3 1.8 ± 1.1 N.D. Pore diameter 47.6% 61.1% 37.5%50.0% 61.1% N.D. distribution value Pore density 75.0 90.0 107.5 8.890.0 N.D. (×10⁻³/μm²)

The film thickness tends to decrease with the increase in the rotationspeed while the film thickness tends to increase with the increase inthe amount of DMSO.

With respect to the total area of the pores, in the case of ethylacetate:DMSO ratio of 100:1, the pore density was considerably low andpore formation was found to become difficult with the increase in therotation speed. In the case of ethyl acetate:DMSO ratio of 100:3, thepore densities were 0.075/μm² (1000 rpm), 0.090/μm² (3000 rpm) and0.11/μm² (5000 rpm), respectively, all of which gave good porousnanosheets, and the pore densities were confirmed to increase with theincrease in the rotation speed. Furthermore, the pore diameters were 2.1μm (1000 rpm), 1.8 μm (3000 rpm) and 1.6 μm (5000 rpm), respectively,which tended to decrease with the increase in the rotation speed. In thecase of 100:5, the pores that became larger due to a lower rotationspeed merged with each other which rendered determination of the poredensity difficult. Determinations of the pore diameter and the poredensity were possible at 5000 rpm. In addition, the conditions of thepores differed between the top and the back surfaces, where the poredensity and diameter were larger at the top surface, with the total porearea being larger at the top surface than at the back surface. Thisseems to be due to the loss of DMSO from the top surface. Similarly, inthe 100:5 system, porous structures could be confirmed at the rearsurfaces at 1000 rpm and 3000 rpm. In general, increase in the rotationrate showed a tendency to reduce the size of the pores and increase thenumber of the pores. Additionally, increase in the content of the poorsolvent (DMSO) increased both the size and the number of the micropores.

In addition, decrease in the rotation rate upon spin coating tended toincrease the pore diameter distribution.

Accordingly, when a polymer for making up the nanosheet was dissolved ina mixed solvent of a good solvent with a low boiling point and a slightamount of a poor solvent with a high boiling point, and the resultantwas then casted by spin coating, a nanosheet having the poor solventdispersed therein was obtained upon removal of the good solvent with alow boiling point. Subsequently, a porous nanosheet was obtained uponremoval of the poor solvent.

Example 3: Method Using Microparticles as Molds for Textured PolymerFilm

All of the manipulations were conducted by placing a spin coater(Opticoat MS-A 100, MIKASA) in a clean room (class 10,000). A siliconsubstrate (KST World) was cut into 2 cm×2 cm, immersed in sulfuricacid/30% hydrogen peroxide water at 120° C. for 10 minutes and thenwashed with deionized water (resistivity 18MΩcm).

polystyrene (PS) microparticles (diameter 913 nm) dispersion(Polysciences) was ten-fold diluted in an aqueous polyvinyl alcoholsolution (Mw: 22,000, Kanto Chemical, 125 mg/mL) and agitated using avortex mixer (VOATEX-2-GENIE, G-560, Scientific Industries). Thesubstrate was placed in the spin coater, a prepared solution was droppedthereon and then subjected to spin coating (1000, 2000, 3000 and 5000rpm) for 60 seconds (room temperature 28° C., humidity 26%).

Subsequently, ethyl acetate was used as a solvent to adjustpoly-D,L-lactic acid (Mw: 300 kDa) to have a final concentration of 30mg/ml. The prepared poly-D,L-lactic acid solution was spin-coated (3000rpm, 60 seconds) on the PS microparticle-fixed PVA film that wasprepared earlier to produce a film (room temperature 28° C., humidity26%). This composite nanosheet was immersed in pure water to dissolvethe PVA film and the PS microparticles to obtain a porouspoly-D,L-lactic acid nanosheet. The porous film was placed in water onceand in a free-standing state, then picked up and placed on a siliconsubstrate with either the top or the back surface facing up, and dried.

Measurement of the film thickness and observation of the surfaces wereconducted with an atomic force microscope (NanoScale Hybrid Microscope,Keyence, tapping mode). The film thickness of the PVA films were 1043 nm(1000 rpm), 782 nm (2000 rpm), 642 nm (3000 rpm) and 533 nm (5000 rpm),respectively, which decreased with the increase in the rotation speed.Moreover, the film thickness of only the poly-D,L-lactic acid nanosheetwas about 200 nm. FIG. 6 shows the AFM images where the systems wereprepared at 1000, 2000, 3000 and 5000 rpm, respectively, from the left:PS microparticle-fixed PVA films (top row: (a1)-(d1)); films obtained bycompositing poly-D,L-lactic acid nanosheets on said PVA films (secondrow: (a2)-(d2)); and top surfaces (third row: (a3)-(d3)) and backsurfaces (fourth row: (a4)-(d4)) of porous poly-D,L-lactic acidnanosheets following removal of PVA films and PS microparticles by watertreatment. Furthermore, the results are shown in Table 5.

TABLE 5 Concentration of microparticles 10-fold dilution of PSmicroparticles Rotation speed 1000 rpm 2000 rpm 3000 rpm 5000 rpm Filmthickness of 1043.0 ± 12.4 782.0 ± 18.2 642.2 ± 22.8 533.7 ± 24.3textured sacrificial film (nm) Film thickness (nm) 218.1 ± 4.8 197.5 ±10.6 215.3 ± 8.7  218.9 ± 9.8  Pore diameter (μm)  0.9 ± 0.4  0.9 ± 0.2 0.9 ± 0.4  0.9 ± 0.3 Pore diameter distribution value 44.4% 22.2% 44.4%33.3% Pore density (×10⁻³/μm²) 82.5   55.3   51.0   47.5  

Therefore, since these PS microparticles have a diameter of 900 nm,their ends are exposed to a more extent for thinner film thickness, andthe pores were confirmed to be widened in the poly-D,L-lactic acidnanosheet according to that exposure. Specifically, exposure of the PSmicroparticles was small at the rotation speed of 1000 nm with smallpores opened at the rear surface of the poly-D,L-lactic acid nanosheetwhile only few penetrated through the top surface. At the rotation speedof 2000 rpm or higher, since the total film thickness of the PVA filmand the poly-D,L-lactic acid nanosheet is less than the size of the PSmicroparticles, the PS microparticles are exposed enough to penetratethrough the poly-D,L-lactic acid nanosheet, where both the top and therear surfaces had similar pores, namely penetrating pores, formed.

Thus, a water-soluble concave-convex film with fixed microparticles wasused as molds. A nanosheet was built on this film and the water-solubleconcave-convex film was dissolved and removed in water to also removethe PS microparticles as well, thereby obtaining a porous ultra-thinfilm.

Example 4: Method Using Precipitated Microparticles as Molds

The poly-D,L-lactic acid was dissolved in ethyl acetate and adjusted tohave a final concentration of 30 mg/mL. Separately, another lithiumbromide microparticles were added and dissolved in ethyl acetate to havea final concentration of 60 mg/mL to prepare a solution. These twosolutions (10 mg/mL) were mixed at a proportion of poly-D,L-lactic acid:lithium bromide ratio=5:1, 5:2, 5:3, 5:4 or 5:5 (w/w). PVA (Mw: 22 kD, 1wt %) was formed on a silicon substrate as a sacrificial film and theneach of the solutions was spin-coated (3000 rpm, 60 seconds). Thedissolved lithium bromide precipitates as ethyl acetate evaporates byspin coating, thereby obtaining a nanosheet containing microcrystals.This was immersed in pure water to dissolve the lithium bromide to peeloff the porous ultra-thin film from the silicon substrate. The resultantwas picked up and placed onto a silicon substrate for AFM observation.The parts where the precipitated lithium bromide dissolved remained andwere observed as the pores. The results are summarized in FIG. 7 andTable 6.

FIG. 7 shows pictures whose poly-D,L-lactic acid: lithium bromide ratiosare 10:1, 10:2, 10:3, 10:4 and 10:5 (v/v), respectively, from the toprow: (a1)-(e1) in the left column are pictures before the removal oflithium bromide, (a2)-(e2) in the second column are pictures wherelithium bromide was removed in water, (a2)′-(e2)′ in the third columnare pictures having the smaller porous regions enlarged ten times, and(a2)″-(e2)″ in the fourth column are pictures having the larger porousregions enlarged ten times. With the increase in the mixture ratio oflithium bromide, the size distribution of the pores tended to becamewider while the number of the pores tended to increase.

TABLE 6 Inorganic salt concentration 10:1 v/v 10:2 v/v 10:3 v/v 10:4 v/v10:5 v/v Rotation speed 3000 rpm Film thickness (nm) 283.0 ± 23.3 275.8± 46.9 262.8 ± 28.7 282.2 ± 76.3 271.8 ± 98.2 Pore diameter (μm)  0.50 ±0.22  0.59 ± 0.44  0.51 ± 0.61  0.60 ± 0.52  0.59 ± 0.63 Pore diameterdistribution 44.0% 74.6% 119.6% 86.7% 106.8% value Pore density (/μm²) 0.37  1.53   1.77  1.84   2.04

Example 5: Ratio of Pore Diameter with Respect to Film Thickness

With respect to the porous nanosheets obtained in the above-describedexamples, the ratios (aspects) of the pore diameters to the filmthicknesses were determined as follows.

$\begin{matrix}{{aspect} = \frac{{pore}\mspace{14mu}{diameter}\mspace{14mu}({nm})}{{film}\mspace{14mu}{thickness}\mspace{14mu}({nm})}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

The ranges of the aspects of the porous nanosheets obtained in theexamples are shown below.

TABLE 7 Production method Aspect range Example 1-1: Method using twotypes 0.787-3.218 of polymers (PS & PMMA) Example 1-2: Method using twotypes  3.255-12.976 of polymers (PS & D,L-PLA) Example 2: Method usingtwo types 1.090-9.771 of solvents Example 3: Method using microparticlesca. 5.235 as molds for textured polymer film Example 4: Method usingmicroparticles 0.990-4.489 as molds (precipitation/crystallization)

Example 6: Method Using Two Types of Polymers (2)

2.0% by weight of polyvinyl alcohol (PVA) (Kanto Chemical) was dissolvedin water. The resulting PVA solution was applied onto one side of apolyethylene terephthalate (PET) substrate film by gravure printing suchthat the film thickness after drying becomes about 60 nm. The PVAsolution was dried in a hot-air drier at 80° C. for 10 seconds toproduce a laminated film which contains the PVA layer on the substratefilm.

Furthermore, poly-D/L-lactic acid (PDLLA) (PURSORB PDL20) andpolystyrene (PS) (Chemco Co., Ltd.) were dissolved in ethyl acetate at2.0% by weight of the total amount of the polymer and at a PDLLA: PSratio of 1:9, 2:8 or 3:7 (w/w). The resulting PDLLA/PS solution wasapplied onto the above-described PVA layer by gravure printing such thatthe film thickness after drying becomes 190 nm. The PDLLA/PS solutionwas dried in a hot-air drier at 50° C. for 10 seconds to produce alaminated film which contains the PDLLA/PS nanosheet on the PVA layer.Table 8 and FIG. 9 summarize the characteristics of the three types ofsystems having different mixture ratios.

TABLE 8 Diameter of Thickness of Thickness of Ratio of PDLLA:PS islandparts island parts sea parts island ratio (μm) (nm) (nm) parts (%) 1:92.3 43.9 132.0 14.2 2:8 8.4 51.8 168.0 37.0 3:7 19.7 100.0 322.2 53.1

FIG. 9 shows AFM images where their PDLLA: PS ratios are 1:9, 2:8 and3:7 (w/w), respectively, from the left. While the shapes of the islandparts were disk-like at the PDLLA: PS ratios of 1:9 and 2:8 (w/w),ribbon shapes were obtained at the PDLLA: PS ratio of 3:7 (w/w).

When the laminated film obtained at the PDLLA: PS ratio of 2:8 wasimmersed together with the substrate film in ion-exchange water, the PVAsacrificial film dissolved and the free-standing PDLLA/PS nanosheetbegan to peel off. The sheet was manipulated with tweezers to be pickedup and placed onto a silicon substrate with either the top or the backsurface facing up. Ethyl acetate is a good solvent for PDLLA but a poorsolvent for PS. When the PDLLA-PS nanosheet on the silicon substrate isimmersed together with the substrate film in ethyl acetate, only thePDLLA regions were selectively removed. Hence, a porous PS nanosheet wasobtained. The PDLLA/PS nanosheets and the porous PS nanosheets wereobserved with an AFM.

Typical AFM images of the resulting PDLLA/PS nanosheets and porous PSnanosheets are shown in FIG. 10. In FIG. 10, (a) and (b) in the top roware the AFM images of the PDLLA/PS nanosheets. The bright regionsrepresent the phase-separated PS regions. In FIG. 10, (b1) and (b2) inthe bottom row are the AFM images of the surfaces of the porous PSnanosheets where the PDLLA regions have been dissolved with ethylacetate to leave the PS regions.

FIG. 11 is a schematic view of the porous PS nanosheets shown in FIGS.10(a′) and 10(b′).

The resulting porous PS nanosheets had a film thickness of 190 nm, withan average pore size of 10 μm (about 5 μm to about 20 μm, pore diameterdistribution value: ±60%) at a density of 6×10⁻³ pores/μm².

The aspect range of the porous PS nanosheets determined according to themethod described in Example 5 was about 10-100.

Now, cyclohexane is a poor solvent for PDLLA but a good solvent for PS.The PDLLA-PS nanosheet obtained on the PET substrate at the PDLLA: PSratio of 2:8 was immersed together with the substrate film incyclohexane, PS was washed, and the resultant was further infiltrated inion-exchange water, thereby obtaining an aqueous solution having afree-standing PDLLA nanodisc mixed. The resultant was subjected tocentrifugation and the resulting concentrated liquid was dropped onto asilicon substrate, dried and observed with an AFM.

Typical AFM images of the resulting PDLLA nanodiscs are shown in FIG.12. All of FIGS. 12(a), 12(b) and 12(c) are the AFM images of PDLLAnanodiscs provided on the same silicon substrate.

FIGS. 12(a) and 12(c) show the AFM images of PDLLA nanodiscs havingmonolayer structures on a silicon substrate, while FIG. 12(b) shows theAFM image of a PDLLA nanodisc having a bilayer structure.

The resulting PDLLA nanodiscs had a film thickness of 59 nm and anaverage diameter of 8 μm (3-12 μm).

Accordingly, two types of polymers that are mutually immiscible in solidstates are dissolved in a common solvent, which is casted to obtain ablend nanosheet that has been phase-separated into a sea-islandstructure, which, in turn, is treated with a good solvent for thepolymer making up the island parts to obtain a porous nanosheet.Moreover, treatment with a good solvent for a polymer making up the seaparts can give a nanodisc.

The invention claimed is:
 1. A substantially disk-shaped ultra-thinpolymer film whose film thickness is 10 nm-1000 nm and whose size is ina range of 30 nm-50 μm, wherein the polymer is a single polymer selectedfrom the group consisting of polymethyl methacrylate, poly-D/L-lacticacid, polyethylene glycol and polyvinylpyrrolidone.
 2. The substantiallydisk-shaped ultra-thin polymer film according to claim 1, wherein thesize is in a range greater than 1 μm and less than or equal to 25 μm. 3.The substantially disk-shaped ultra-thin polymer film according to claim2, wherein the size is in a range greater than 1 μm and less than orequal to 15 μm.
 4. The substantially disk-shaped ultra-thin polymer filmaccording to claim 1, wherein the polymer is poly-D/L-lactic acid.